The Roboutian Heresy

by Zahariel

Inspired by the great Dornian Heresy of Aurelius Rex, here is an alternate timeline to the Warhammer 40000 universe, where Guilliman turned traitor instead of Horus, and led half the Legions in rebellion against the Emperor. The Index Astartes are done for all Legions. Now, the Times of Ending have begun ... Also has a TV Tropes page now !

15. Index Astartes : Sons of Horus

I do not own the Warhammer 40000 universe nor any of its characters. They belong to Games Workshop.

Inspired by the Dornian Heresy, by Aurelius Rex.

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Index Astartes – Sons of Horus : Brothers in Glory and Grief

Among the nine Legions which stayed faithful to the Emperor, the Sons of Horus are hailed across the Imperium as the greatest. Warriors without equal, they still hold to their heart the ideals of the Great Crusade, forever fighting to expand the Imperium's borders. There are few warriors as revered and feared as them in the galaxy, and the legacy of the First Warmaster still echoes today on a million worlds. Yet the shadow of their fallen Primarch looms over all scions of the Sixteenth, driving them to bouts of melancholy and unbridled fury. Horus' fall during the Siege haunts the memory of Lupercal's sons, forming a tale illustrating both the Legion's greatest strength and its greatest weakness : passion. Grudges ten thousand years old are still waiting to be paid, and the Sons of Horus are still waging their millennia-long feud against their own twisted reflection, born of the Primogenitor's madness in the dark days of the Clone Wars. But on the field of battle, there are few others the Imperial forces battling the darkness among the stars would want at their side more than the Sixteenth Legion.

Origins

For ten thousand years, Imperial historians and philosophers alike have wondered : what would have happened if the Dark Gods had not stolen the Primarchs from the Emperor, scattering them across the galaxy while they were still infants ? How different would the galaxy be, had the twenty sons of the Master of Mankind been raised as He intended ?

We will never know the answer to that question, and to ponder it too deeply is to court madness and delusion, the mind shattered by grief at all that was lost. But a glimpse of the glories that would have been can still be seen, by looking at the one Primarch who was raised by the Emperor : Horus Lupercal, greatest of the Emperor's sons, First Warmaster of the Imperium and Primarch of the Sixteenth Legion. Unlike some other Primarchs, the life of Horus is well-remembered in the Imperium, most notably thanks to the extensive account he himself gave to the famous remembrancer Petronella Vivar during the Great Crusade.

Like all Primarchs, Horus was taken from the Emperor when he was still an infant, and his life-pod crashed on the dying mining world of Chthonia, barely a few light-years away from Terra. Once, Chthonia had been a planet rich in minerals and other precious resources, but decades of ruthless exploitation had left it all but barren, and its population suffered from poverty, starvation, and pollution. Entire hive-cities had descended into anarchy, as dozens of gangs fought each other over the scraps that remained. The rich and powerful elite had long departed the world, abandoning Chthonia in a state of complete lawlessness. The planet itself was on the verge of collapse, its structural integrity damaged by the careless mining.

The only societal structure left on the planet was the gangs, who fought in the tunnels and on the surface alike. Ruled by the strongest, these gangs varied in size from a handful of raiders to tens of thousands of humans toughened by a lifetime of conflict, holding power comparable to that of the techno-barbarians of Terra themselves. Every single one of these primitive cultures was brutal and unforgiving, but as in all things, there were degrees in Chthonia's savagery : some gangs held the group above the individual, while others were little more than packs of jackals, ready to betray one another at the first opportunity.

In that environment, Horus, though barely a child by human standards, survived and even thrived. For three years, the young Primarch learned the brutal ways of the Chthonian people, living in the shadows. Already, a sense of justice began to manifest in him, and several gangs started to exchange whispered rumors of a child that could defeat ten men twice his size alone, who attacked those who preyed upon weaker humans. But before Horus could even reach adolescence, the Emperor arrived to Chthonia, sensing the presence of one of His children on the desolate planet.

The gangs of Chthonia reacted violently to the sudden arrival of so many strangers, after so long spent in total isolation. From the moment the Emperor and his Custodians set foot on the planet, they were beset by ambushes and attacks as gang leaders roused their followers to war against the intruders. Of course, none of them were any threat to the Emperor, and thousands were slain before Horus was found. The young Primarch, upon hearing of the strangers' arrival, felt in his heart that he was the reason for it, and came forward to face whoever had travelled so far to find him.

Horus met his father and His guards amongst the bleeding remnants of the latest ambush, standing tall and proud in front of the golden giants. What transpired between them during that first meeting is unknown, but Horus left Chthonia soon after aboard the Emperor's personal flagship, Bucephalus.

It was like looking at the sun for the first time and realize everything you had missed away from its light.

In later years, when asked how to describe his first meeting with the Emperor, Horus would use these words, though he knew they failed to truly carry what he had felt that day. The man radiated a kind of light that warmed up the soul, an aura that carried within it the promise of a better future. He smiled when he saw the boy, and Horus felt his heart tighten at the sight. How lonely had that man been, that merely seeing him would make him smile like that ?

'Hello, Horus,' he said, and the golden light was gone, revealing an old, old man who was so, so very tired. 'I am glad to finally meet you. I am your father.'

Not just the young Primarch left Chthonia that day, however. Many among the Emperor's retinue called for the planet's destruction, to punish its inhabitants for their crime of daring to assault the Master of Mankind. The Emperor, however, respected the courage of the gangers, misplaced as it might have been, and instead ordered that the planet become a recruiting ground for the Imperium. The Great Crusade had barely begun, and it would need a great many soldiers – soldiers as determined and though as the people of Chthonia. Tens of thousands of gangers vanished alongside Horus, most of them to be transformed under the gene-chirurgeons' attentions to be reborn as warriors of the newly formed Sixteenth Space Marine Legion. Others were trained and formed into several contingents of elite troopers, who would go on to become some of the most famous of the Imperial Army's Regiments.

Having found one of His sons far closer to Terra than He had anticipated, the Emperor began to educate him immediately. The best tutors of the Imperium were called upon, teaching Horus all that they knew, while the Emperor Himself shared His knowledge of the galaxy with His son. However, the Master of Mankind refrained from sharing some secrets with Horus : He didn't tell the young Primarch of the threat of Chaos, of the Ruinous Powers and the daemons that serve them. Whether He came to regret it centuries later, we cannot know. He did share His vision of the galaxy, though : an Imperium strong and free from the threats of the xenos, no longer blinded by superstition nor foolishly devoted to technology. Many sacrifices had already been made in the name of that vision, and many more would be required before it became a reality, but the Emperor promised His son that one day, with his help, they would make it so.

Horus learned everything he was taught, and a lot more besides. He frequently left his quarters aboard the Bucephalus to explore the rest of the ship, watching the first lords of the Great Crusade gather and plan the conquest of the galaxy. On several such occasions, these warlords were surprised to see the youth emerge from the shadows and point out a flaw in their plans before vanishing once more.

The quickly-growing child also witnessed the negotiations and politics between the various factions of the Imperium – including the consequences their feuds could have for those under their command. It is believed that it was during this period that the Primarch developed the distaste of petty politicians and courtiers that, though well hidden, would always accompany his dealings with the Administratum and all leaders who put their own position and power above the needs of those under their authority.

Intense physical training was also part of Horus' education, though like all Primarchs, he had an instinctual understanding of such things that put most of his would-be instructors to shame. He was trained in battle-arts both developed amidst the warring chaos of the Age of Strife and inherited from master to apprentice for tens of thousands of years. He was made to perform feats of endurance that would have killed a Space Marine, and fought combat servitors that the techno-priests of the Mechanicum had – at his own demand – designed to kill him. But no matter how hard the challenge, Horus triumphed. Those who were involved in his education began to develop an almost religious respect for the young Primarch, and as rumors of his prowess spread, efforts to locate his brothers intensified.

While Horus was being groomed as a leader of the Great Crusade, the Sixteenth Legion was also being prepared. Children from Chthonia formed the bulk of the new aspirants, and its numbers swelled until, just as Horus emerged from adolescence and into his full power as a Primarch, it was ready for full deployment. The First Primarch, as Horus was already known to those who were aware of his existence, was brought by the Emperor to those who bore his gene-seed. It was time for him to take command of the Legion that had been forged in his image, and lead it to glory and conquest in the Great Crusade.

The Great Crusade : First Among Equals

When the Emperor had lost Horus and his brothers to the machinations of the Warp, He had used the research and samples still in His possession to create the first Astartes. For this, He needed male children strong and genetically pure enough to bear the trials of the process, and He looked form them across the surface of unified Terra. Those who bore the genetic imprint of the sixteenth infant were from hunter-clans, regardless of whether their tribes had survived in jungles or in slums. All of them, without exception, were of humble birth, tested since their childhood by a harsh environment. This made them pragmatic and devoted to the group rather than the individual, though they still had dreams of their own.

The first deployment of the Sixteenth Legion occurred long before Horus was discovered, when the Emperor had completed the unification of Terra and turned His eyes to the rest of the Sol System. The clans of Luna, Terra's single moon, had great knowledge of genetic lore, and the Master of Mankind desired that expertise and facilities to help in the expansion of His Legions. However, the clans, who called themselves the Selenar, had maintained their independence from Terran techno-barbarians and magos alike for centuries. Though they welcomed His ambassadors, they refused the Emperor's offer to become part of the Imperium, secretly laughing at the Imperial Truth. In response, the Master of Mankind decided to send three of His Legions – the Seventh, the Thirteenth, and the Sixteenth – to bring them to compliance by military means.

The Selenar Gene-Cults

No one knows how old the cults of Luna truly were when the Emperor first revealed Himself on warring Terra. They had occupied the moon for as long as anyone living remembered, and since Mankind has had the capabilities of travelling to Luna as soon as the end of M2, there is a very large gap in history as to when lunar colonization began and when the cults appeared.

What is known is that the Gene-cults were fanatic followers of a strange and unholy religion. They used their technological knowledge to pursue immortality through genetic reincarnation, somehow managing to preserve the experiences from one incarnation to the next. This echoed with their cult's belief that every human being is merely a reflection of some over-reaching archetype. Each of the cults focused on a different archetype, some inspired by legends and myths, others so alien that rumors grew that the Selenar had been influenced by xenos contacts prior to the Age of Strife.

After the First Pacification of Luna, the Selenar bowed to the authority of the Imperium and assisted in the extension of the Space Marine Legions. Over the two centuries of the Great Crusade, hundreds of thousands of Legionaries were transformed in their genetic facilities, until the Legions each developed their own structures for processing their recruits. This led to the cults slowly losing their use to the Imperium, and while the Emperor, and later the High Lords of Terra, have kept to the agreement that was reached after the First Pacification, their numbers diminished over the years. Eventually, the Gene-cults died out, their domed cities left alone on the Terran moon. Many tech-priests have attempted to breach them and claim the secrets that remain hidden there, but few have returned alive – the last of the Selenar left safeguards to preserve the legacy of their kin from plunderers.

There are rumors that not all Selenar accepted their submission to the Imperium. According to tales that are only accessible to the most highly-ranked Inquisitors, it was a group of such disgruntled gene-wrights who sabotaged the gene-seed of the Third Legion soon after its inception, leading to the catastrophic losses the Emperor's Children suffered before their Primarch was found. According to these hidden texts, the reason the war waged by the Sixteenth Legion on Luna is known as the "First" Pacification is because, following this act of treachery, the Emperor sent the Third Legion to wage a second war against the rebels, one that was erased from almost every record to preserve the Selenar cults who had remained faithful to their oaths.

As soon as they realised that the time of diplomacy had passed, the gene-cults prepared for war. Their usual divisions were quickly cast aside in the face of the possibility of losing their independence, and when the Legions arrived to Luna, they found their foes ready. The Sixteenth Legion had been chosen to be the vanguard of the assault, and they struck will all the fury that would become legendary in centuries to come. The anti-orbital weapons of the cults, marked by spies hidden amongst the diplomatic envoys, were destroyed by squads of Astartes, and the warriors then spread in the subterranean tunnels of the cults, butchering all those they came across. The cults fought back with their gene-wrights, genetically altered beings designed for conflict, but they were no match for those who had received the Emperor's own alterations. Soon, the two other Legions began to advance and seize the genetic facilities, finding their defenders terrified and broken.

After a few hours, the leaders of the gene-cults called out to the Emperor, begging Him to stop the killers He had let loose in their midst. The words "Call back your wolves !" became part of the Sixteenth Legion's folklore, and soon after the First Pacification of Luna, the Emperor Himself bestowed these warriors with the name of 'Luna Wolves', in acknowledgement of the great service they had done the Imperium that day.

With the genetic facilities secured and the compliance of the gene-cults enforced, the Legions could now grow to match the needs of the Imperium. The first Chthonian recruits became Luna Wolves on the very moon that gave the Legion its name, and when they were ready, the Emperor brought Horus to them so that he might take command.

Under the leadership of their Primarch, the Luna Wolves left the Sol system to take their rightful place at the Great Crusade's forefront. More worlds were conquered by them than by any other Legion, though their way of making war often left the worlds in their wake crippled. The Luna Wolves kept following the same tactics they had used on Luna, and before that in the gang wars of Chthonia : they went directly for the enemy leader, not hesitating to use excessive force to end a conflict as quickly as possible. While the infrastructure of the worlds they brought to compliance was often more or less spared from the destruction, the hierarchy was always beheaded, leaving the Imperial adepts sent after them with a much harder task of integrating the planet into the Imperium.

The Lupercal Tank

It was during the Great Crusade that the Quest for Knowledge of the Adeptus Mechanicus began. This sacred undertaking, still unfinished after ten thousand years, has the goal of gathering all the lost STC schematics used by Mankind during the Dark Age of Technology. These templates are more valuable than entire worlds, and the Mechanicus has been known to start wars at the mere rumour of their presence.

As the Imperium expanded, many of the worlds brought to compliance were found to have some STC left on them from before the Age of Strife. The Mechanicus greedily reclaimed them, as part of the pact that was forged between the tech-priests of Mars and the Emperor. While some of these templates were part of forbidden branches of technology and others were buried within temples, never to see the light of day, many were incorporated into the new Imperium, to serve in the effort of the Great Crusade. One of such designs was the Lupercal Tank, so named after the aggression displayed by the Sixteenth Legion.

Used to this day by almost every regiment of the Imperial Guard – bar those from worlds too technologically regressed to be able to use it – the Lupercal Tank is incredibly versatile. It can be adapted for almost any kind of battleground, from the streets of a hive-city to the dunes of a chemical wasteland. Weapons can also be replaced easily, learning to drive it is ridiculously easy, and it can run on anything even remotely fuel-like. Forge-worlds churn out billions of these war engines every year, and they are used across the galaxy to fight the many enemies of the Imperium.

Not all human worlds found by the Expeditionary Fleets led by the Luna Wolves were conquered, of course. On many worlds, the words of the iterators were able to convince the population to embrace the Imperial Truth and join the growing Imperium not in violence, but in celebration. In the case of the Expeditionary Fleets that Horus himself led, it was very rare for human worlds to refuse integration into the Imperium indeed. The charisma of the First Primarch was almost impossible to resist, even for Legionaries. Many planetary leaders intent on politely refusing the offer to join the Imperium left the meeting wondering why they had even wanted to do such a thing in the first place, convinced of the righteousness of the Imperium.

As the Great Crusade went on, the lost Primarchs were rediscovered one after the other. Horus made sure to meet each of them when he wasn't present at their discovery, and through his charisma, formed strong bonds with all of them. Even bitter Corax and prideful Vulkan couldn't help but like their elder brother, and it is said that all of them, in private at least, acknowledged that he was the greatest among them. Still, there were those brothers with whom Horus had an especially close relationship. Among those was Fulgrim, for Lupercal and the Phoenician forged their bonds of brotherhood in the fire of battle and conquest.

When Fulgrim was found on the world of Chemos and given command of his own Legion, his sons were too few form him to operate alone. The Third Legion – named the Emperor's Children, in acknowledgement of their Primarch's devotion – fought at the side of Horus in the Great Crusade, with Lupercal and the Phoenician forging a bond of brotherhood that transcended their blood ties. After fifty years of conquest, the numbers of the Third Legion had reached the level where they could operate on their own, and the two Primarchs parted ways after them and their sons had renewed their oaths of brotherhood and sworn to come to each others' aid if the need ever arose.

Soon after that parting, the Luna Wolves arrived to the world of Davin. With them came a contingent of Word Bearers, whose Primarch Lorgar had recently been found on the arid world of Colchis. Leading the warriors of the Seventeenth Legion was Erebus, one of the first Chaplains to have risen from the Primarch's homeworld.

Davin was a world populated by primitive tribes, many of which had devolved over the centuries of isolation into something that wasn't quite human. Despite this, and their primitive level of technology, they fought against the Legionaries with great courage, impressing even Lupercal with their bravery. Horus was convinced that the tribes could be made to see reason and join the Imperium peacefully – and some clans even surrendered and helped the Imperium fight their fellow Davinites soon after the beginning of the campain. However, Erebus came to the Primarch, telling him that he had watched the rites and beliefs of the Davinites, and that they reminded him of the cults that had held his homeworld's people captive for centuries before the coming of Lorgar.

'There is a sickness hiding beneath the surface of this world, my lord. We must purge it with fire, rather than allow it to endure, or try to treat it with words.'
Erebus' words to Horus Lupercal, on the Davinite tribes

Erebus convinced Horus that the planet had to be cleansed of these religious beliefs, and that none of its corruption could be allowed to spread. He told the Primarch of the human sacrifices performed by the Davinite tribes "allied" to the Imperium where the Legions couldn't see them. He warned that these tribes were only pretending to join the Imperium, sacrificing their own in order to protect their twisted lifestyles. With heavy heart, Horus accepted the evidence presented by the Word Bearer, and the tribes of Davin were broken upon the anvil of war. The survivors were gathered in great camps while every trace of their belief system was ruthlessly expunged by the Word Bearers. It is said that the Luna Wolves, when they saw the fervour with which their cousins were destroying an entire culture, felt something akin to fear for the first time since their Ascension.

Several decades after the departure of the two Legions, the Magos Biologis detached to the Imperial settlement on Davin declared that the entire population of the tribes was genetically corrupt. They were too deviant from the purity of the human genome to be even attributed the statute of abhuman that had been bestowed upon other mutated strains. The entire population was eliminated, and new colonists were brought to Davin – though the world has, to this day, retained a dark reputation.

Several decades later, at the turn of the millennium, the Great Crusade peaked with the Ullanor Crusade. After years of fighting back the Waaaagh ! of the Ork empire led by Urlakk Urg, Perturabo had called for his brothers' aid in defeating the xenos Warboss. His call was answered not just by Horus, but also by Jaghatai Khan and even the Master of Mankind Himself, accompanied by His Custodes.

With the strength of three Legions and the Emperor's own guardians, the Imperium crushed the bestial empire of Urlakk. The Iron Warriors grounded the Orks to paste, while the White Scars sowed confusion and discord among their lines with lightning strikes. Horus and the Emperor, for their part, struck together at the very heart of the green horde. Back to back, the Master of Mankind and the First Primarch descended upon Urg's fortress, and slew the Ork Warboss. This glorious moment is immortalised on one of the walls of Lupercal's Cathedral on Terra, where the two greatest heroes of Mankind are depicted striking as one against the xenos beast. It is said that any who look upon the wondrous image cannot help but weep, both at the magnificence on display and in sorrow that it will never be again.

After the death of Urlakk Urg, the Ork empire of Ullanor was broken, and the planet purged of greenskins entirely. This marked the destruction of the last great xenos dominion capable of presenting a threat to the Imperium as a whole. There remained many alien empires to break, many human worlds to bring into the fold, but the last known threat to the Emperor's vision had been beaten. The victory at Ullanor heralded a new age for Mankind, and the Emperor ordered that a great Triumph be held in celebration. Mountains were razed, oceans drained, and avenues the size of continents were traced on the perfectly flat surface that was left behind them. Upon those defiled billions of Imperial soldiers, hundreds of thousands of Legionaries, and Titans of Legios from forge-worlds across the entire galaxy.

Though we do not know whether or not their brotherhood was complete, it is known to us that most of the Primarchs were there as well. They watched the Triumph, which had become more of a celebration of the entire Great Crusade than merely of the victory at Ullanor. Then, at the surprise of all those present, the Emperor announced His intent to withdraw from the front of the Crusade and return to Terra, where a great work awaited Him. Despite the protests of Angron and others, the Master of Mankind was inflexible. He named Horus the Warmaster of the Imperium, supreme commander of the Great Crusade. To Lupercal now would fall the task of coordinating the greatest endeavour in the history of Humanity.

Humbled and shocked, Hours accepted the honor his father had bestowed upon him, vowing that he would not fail His expectations. To mark this change from one Primarch among others to the leader of the entire Imperium's military might, the Sixteenth Legion was renamed from the Luna Wolves into the Sons of Horus. The Emperor also declared that Magnus would return with Him to Terra, alongside the greatest scholars of his Legion – safe for Ahriman, the First Captain, who would lead the rest of the Fifteenth Legion and join with Horus to assist him in his new duties.

'I cannot tell you my plans, Horus. Not yet. Until I and Magnus know for sure that what I intend is truly possible, I refuse to burden you with hope that may prove false. If I fail … If I cannot complete my grand vision, then it will fall to you and your brothers to guide Mankind, my son. You must find your own path, your own dream, your own ideal, so that if mine cannot become true, you will have the strength to make yours a reality.'

It was soon after the Triumph that Guilliman, bitter at not having been chosen, asked Horus the permission to take his own Expeditionary Fleet, the 12th, and go out beyond the borders of known space. Horus, seeing the wound on his brother's pride, allowed it, believing that Roboute's temper would cool during his journey. Ultimately, this would prove a terrible mistake, but at the time, Horus genuinely believed that Guilliman's anger would pass – and it probably would have, had the Dark Gods not conspired to twist the heart of the Avenging Son.

As Warmaster, Horus continued to uphold diplomacy as the first approach to any human culture, stating that "there are enough xenos in the galaxy that want to destroy Mankind without us killing each other". Under the influence of his brother Curze, he also tried to soften the general approach of the Imperium to human worlds, seeking to make sure that violence was always employed only as a last resort. He had various degrees of success – even the reach of a Warmaster wasn't large enough to touch every corner of the galaxy at once – but never ceased in his effort, supported by those of his brothers who believed in his vision.

However, Horus also showed a great distrust for the Council of Terra his father had appointed to direct the Imperium in His absence. To Horus, the civilians who sat there were unworthy of their rank and had only obtained them through political manoeuvring and because the organizations they represented were needed by the Imperium. Malcador the Sigillite was the only member he respected, and even then he believed that the old man had been exposed to politics too long. In Horus' eyes, the greed and ambition of the other High Lords endangered the entire Great Crusade and by extension the Imperium, notably by enforcing taxation upon recently conquered worlds before they were fully integrated into the empire. Ten thousand years later, this attitude is still displayed by his sons – in fact, considering the nature of the Administratum, it is actually much worse.

After several years spent keeping the various elements of the Great Crusade together while also struggling to continue his own military campains and with more and more friction appearing between his brothers, Horus was drawn to the world of Murder by a distress call from a Blood Angels' force. With him came the Sixty-Third Expeditionary Fleet, and that world would be the first step on a journey that would take Horus beyond the limits of everything had believed possible and into a new realm of dark truths and terrible knowledge.

The Interex : Unwelcome Revelations

'This. World. Is. Murder.'
Last transmission from Captain Khitas Frome of the Blood Angels, leader of the 140th Expeditionary Fleet.

The Sons of Horus and Thousand Sons weren't the only ones to have heard the call for aid of the Blood Angels. Before them, a force of Emperor's Children led by Lord-Commander Eidolon had arrived, determined to rescue their cousins from the planet. Eidolon ordered his forces to make planetfall immediately, despite the risks – some say it was because he didn't want to waste time in rescuing the Blood Angels, others, less charitably, claim that he refused to share the glory with the Sons of Horus, whose arrival had been announced by the astropathic choir.

However, the Emperor's Children were decimated by the very same foe that had slaughtered the Blood Angels in their entirety. Murder was home to a vicious species of hive insects, that the Imperial forces soon came to call the megarachnids. These insect-like creatures were armed with armsblades capable of tearing through power armor as if it were paper, while the storms raging permanently over the planet had scattered the Emperor's Children and the dense forests forced the isolated groups to remain on edge permanently. When the reinforcements arrived, Eidolon had already died, leaving Captain Saul Tarvitz in command of what little forces he had managed to gather. Only a desperate action of Saul – taking down one of the megarachnids' great trees, upon which they had hung the bodies of the Blood Angels and Emperor's Children – resulted in an opening in the storm clouds, and allowed the Sons of Horus to reinforce their allies.

What followed was a brief but bloody campaign, as the forces under Horus' command extracted the surviving Emperor's Children and prepared for the extermination of the megarachnids. But soon after Tarvitz and his remaining brothers had left the system to return the body of their Lord-Commander to Fulgrim, a fleet arrived to Murder – or, as they called it, Urisarach.

The Mournival at the time of the Interex Incident
Ezekyle Abaddon – Captain of the First Company, leader of the Justaerin
Tarik Torgaddon – Captain of the Second Company
Horus Aximand – Captain of the Fifth Company, known as "Little Horus"
Gavriel Loken – Captain of the Tenth Company

These newcomers were envoys of a human civilization that the Imperium hadn't met until now. Calling themselves the Interex, these humans had survived through the Age of Strife while maintaining a high technological level. However, they had also allied with various xenos species, including the all but extinct kinebrach, a race that had nearly destroyed itself in past ages and now existed under the protection of the Interex. Unlike the Imperium, the Interex did not believe that all alien species needed to be wiped out : indeed, they had defeated the megarachnids in war, but instead of exterminating them, they had brought the survivors to Urisarach, where they could live in peace and not be a threat to anyone else.

Meeting a civilization with beliefs so contrary to the Imperial Truth was a shock to the Sons of Horus, but less so for the Thousand Sons, who knew much more of Mankind's secret history. Many in the Legion called for war against the Interex, for had the Emperor not declared that Mankind could not coexist with xenos breeds ? But Horus, advised by his calmer sons and Ahriman, refused to listen to them, remembering the words his father had left him before returning to Terra. The Warmaster wanted to bring the Interex in the Imperium, but he also believed that the Imperium could learn from that civilization. After all, Mankind was no longer threatened with extinction at xenos hands – with the victory at Ullanor, the last great alien empire had been destroyed. Humanity was now stronger than ever – perhaps there was no need to wipe out anymore other species.

Horus and the Interex envoys agreed to a diplomatic summit on the Interex homeworld, while the fleet of the Sixteenth Legion waited at the system's edge. Despite the implicit threat caused by the presence of such an awesome force, negotiations progressed relatively well, though the Interex diplomats were wary of the Imperium's overly military attitude. It soon became evident that direct integration would be difficult, but Horus believed that the two galactic powers could at least be allies, and eventually, over the course of generations, peacefully become one. But that hope was not to be.

The killer looked at the blade, turning it so that it reflected the light. It was beautiful in a way no other weapon he had ever wielded – and he had wielded a great many – could ever hope to be. He fancied that he could hear the weapon whisper at the back of his mind, telling him its desire to be used once more rather than left to gather dust.

Soon, he promised it. Soon.

He departed in the shadows, leaving behind him the corpses of the museum guardians. These fools had had no chance to stop him at all, and in truth he could have taken what he needed without killing them … But their deaths would ensure that war would erupt between the Sons of Horus and the Interex. One way or another, they would serve the cause of Chaos – such was the will of his lord, Lion El'Jonson ...

Eventually, several days of continued negotiations were brought to an end by the need of the Interex representatives to rest and discuss with one another. As Horus returned to his quarters, he was attacked by an assassin, and struck by a kinebrach blade that, despite all of his resilience, brought him down unconscious. Soon after, just as the Apothecaries began to work to rouse their Primarch, the Interex representatives arrived, incensed, claiming that one of their museum had been breached and one of the weapons stored there stolen, accusing the Imperium of the theft. For a brief and dreadful moment, it seemed that war would erupt, as First Captain Abaddon was enraged at what he perceived as a blatant attempt to get way with the murder of his father, but the rest of the Mournival restrained his rage. When the Astartes told the Interex representatives of the assassination attempt, they immediately realized their mistake, and after apologizing, they declared that this must be some attempt by the agents of "Kaos" to sow discord and hatred between the Interex and the Imperium.

At first, the Sons of Horus believed that "Kaos" was an enemy of the Interex, and returned to praying for their Primarch's survival. However, a discussion between Garviel Loken, newest member of the Mournival, and one of the Interex soldiers, revealed that it was much more. Having already been exposed to the malevolence of the Warp in a previous campaign, Loken believed what most Imperials would have dismissed as superstition, and brought Ahriman to the discussion. As soon as the first Captain of the Thousand Sons descended from orbit, he sensed the Warp corruption clinging to Horus. The wound caused by the kinebrach blade had created an opening in the Warmaster's mind, allowing for the creatures of the Warp to go in. Horus was still fighting against them, but to save him, the Space Marines needed to go there too and rescue the Primarch's soul from those who attacked it.

Ahriman immediately gathered his most powerful and skilled Librarians, and together, they sent the minds of the Mournival, the closest and greatest sons of Lupercal, into the psychic battlefield that Horus' soul had become. We know not what they saw there, only that the battle was fierce, and ended with the victory of the forces of righteousness, as Horus cast off the shackles of Chaos, defiantly proclaiming to the very face of the Dark Gods that he would never be theirs.

They were wolves running through a plain, searching for their alpha.

Above them, the skies were torn with unnatural storms, and the stench of death and decay was heavy in the air. But they didn't care. All four of them ran, on and on, seeking the one they loved more than any other. A young boy ran with them, too, an ally to the pack, though he was not one of them. He was guiding them through this treacherous place, away from the pits and the traps, and toward their goal.

Then they found the alpha. Four great and terrible beasts were fighting him, each a nightmarish abomination that had no place in a sane universe. Howling together, the pack mates hurled themselves at the beasts, their fangs and claws tearing at their flesh. At their side, the boy charged as well, holding a spear in his hands that he rammed into the side of some avian monstrosity.

The beasts roared their pain and hatred, and turned toward the pack. Between them, the great wolf, the alpha, rose to his feet, bleeding but unbroken, light shining in his golden eyes. His jaw opened and he howled, the sky itself trembling at the sheer power of the declaration …

Freed from the clutches of the Warp, Horus rose, still weakened by his trial, but burning with a new determination. He had gained terrible knowledge during his time captive, and needed to return to Terra at once, to bring word of the threat of Chaos to the Emperor. The daemons that had tortured his soul had also whispered of him of some great and damnable plot, soon to reach fruition, that would bring low all that the Great Crusade had built. All of this, the Emperor needed to know, and so Horus left the Interex, vowing to return one day to continue negotiations, and warning them of the threat he had been told of.

The Fate of the Interex

After the end of the Heresy, the Sons of Horus returned to Interex space, determined to honor their Primarch's promise. But all that they found there were destroyed worlds, their population slain in hideous scenes of carnage and their riches plundered. A civilization that had endured for thousands of years had been wiped out, but who was responsible for it remains unclear. Most Imperial scholars put the blame on the Dark Angels, or some other traitor force sent to prevent the Interex from intervening in the civil war ravaging the Imperium. However, one should remember that Chaos has many pawns, and it is entirely possible that the force that the Dark Gods sent to destroy the Interex didn't belong to the Traitor Legions, or even to Mankind …

The journey back to Terra was long and difficult, with the Warp in turmoil preventing passage through many known routes and forcing the Navigators to take risks. Eventually, Horus and his men reached Sol, only to be greeted with terrible news : Guilliman had turned against the Emperor, and with him, Sanguinius, Rogal Dorn, and Ferrus Manus.

The Heresy : Treachery in the Dark

When he heard the news of his brother's treachery, Horus' first reaction was to order his Legion to prepare for immediate departure, that he might crush Guilliman and his cohorts himself. However, his reason soon caught up to his rage, as he realized the extant of the damage his fleet had taken, the distance separating him from Isstvan, and the likely influence of Chaos in the whole affair. Worse was the fact that the war had already arrived in the Solar system : Mars, heart of the Mechanicum, was torn apart by civil war between arch-magi supporting the rebellion and those who had remained loyal.

After several hours of reflection and discussion with the Emperor, Magnus, and his Mournival, Horus decided to send an astropathic message to every Legion who had remained loyal. To Angron and Lorgar, he commanded they go to the Five Hundred Worlds, Guilliman's fiefdom in the Imperium, and make sure that their resources weren't used to support the rebellion. The remaining Legions – the Dark Angels, White Scars, Night Lords, Death Guard, Salamanders, Raven Guard and Alpha Legion – were ordered to go to the Isstvan system at all speed. There they would confront the Traitor Legions and their allies and bring them to justice.

Soon after the message had been sent, warnings came from all over the Solar Segmentum. As the news of Guilliman's rebellion had spread, entire systems had declared themselves for the turncoat son, and cut off contact with Terra. Horus divided his Legion in several fleets and sent them to punish these traitors closer from the Throneworld, while also combining his efforts with the Custodes and the Officio Assassinorum to locate hidden spies and infiltrators hiding within the incredibly complex structure of Terran society.

Even as Horus struggled to maintain order across the Solar Segmentum, more terrible news kept reaching him. First, the Emperor and Magnus vanished in the tunnels beneath the Imperial Palace, fighting a war against the daemonic legions that poured through the shattered Webway Gate. Then, the survivors of Prospero arrived, and with them came the news of the Space Wolves' betrayal. The prospect of the Legions sent to Isstvan facing the Wolves as well as the four known Traitor Legions was worrying, but such was the turmoil in the Warp that sending a warning to the retribution fleet was all but impossible.

A few weeks later, Perturabo returned from Olympia, and it fell to Horus to tell his brother what had transpired in his absence. Enraged, the Lord of Iron nonetheless listened to the Warmaster, and sent thirty thousands of his warriors, under the command of one of his Triarchs, Barban Falk, to free Mars from the rebel arch-magi and their armies of tech-horrors. Meanwhile, Perturabo would fortify the Imperial Palace, in the unlikely event that the war somehow reached the Throneworld.

The most terrible news, however, was the reports that soon arrived from Isstvan, carried upon the tumultuous tides of the Warp ahead of the few survivors of the disaster that had occurred there. Four of the seven Legions sent at Isstvan – the Dark Angels, the White Scars, the Salamanders and the Raven Guard – had revealed themselves as accomplices of Guilliman's treachery, and had all but destroyed the loyalist forces who had fought the traitors on Isstvan V. Konrad Curze was dead, Alpharius was missing, and most of the Death Guard had perished. At the same time, the Word Bearers and World Eaters had been cut off from the rest of the Imperium as a massive Warp Storm erupted within the Five Hundred Worlds, trapping them in the hell Guilliman's kingdom had become. The Ultramarines began to advance toward Terra, while their allies scattered across the galaxy in pursuit of their own dark agendas.

There were some among Horus' circle of advisers who wanted to take the Legion and meet the Ultramarines head-on, to crush them while they were isolated from the rest of the traitors. But the Warmaster knew that, for all the strength of his sons, they wouldn't be able to match Guilliman's Warp-infused Legionaries in open battle – not with the Iron Hands fighting at their side. Though it tore at his heart, Horus knew that the only chance the loyalists had to defeat the traitors was to wait on Terra, hoping that the two Legions he had sent to Ultramar managed to escape from the Ruinstorm. The worlds on the path of the Traitor Legions would burn, though the scattered Night Lords and Alpha Legion would fight alongside their defenders to the death.

'Warmaster … That is what it means, brother. The strength to do what must be done.'
Attributed to Horus Lupercal, during the Roboutian Heresy

Several years passed before the Traitor Legions arrived to Terra. All that time, Horus sat within the Imperial Palace, directing the efforts of his Legion to keep the Solar Segmentum from falling apart and listening to what few reports made it through the Warp, speaking of the atrocities unleashed by the renegades upon the worlds that resisted them – as well as many who didn't. From these fragments of abomination and the knowledge of Chaos he had gained during his brief possession, Horus identified which of the Traitor Legions had succumbed to which power of the Warp. This knowledge would prove useful during the Siege.

The Sons of Horus were far from inactive during that period. They were all over the Segmentum, helping the Iron Warriors build the defenses of the Sol system and hunting down infiltrators and outright rebels. They stopped a rebellion in the hives of Merica, whose rulers had long chaffed under the yoke of Imperial rule and saw Guilliman's uprising as their chance to reclaim their independence. Unknown to them, the emissaries sent by the Arch-Traitor to foster their resentment were actually daemonhosts, and when the Sons of Horus stormed the would-be rebels' strongholds, they revealed themselves in all their terrible glory. In the ensuing bloodbath, several bloodlines that had ruled the continent for millenia were wiped out, and the population of Merica returned to the fold of the Imperium.

Many other skirmishes were fought before the Traitor armada arrived. Flotilla were sent ahead of the main fleet – stolen vessels packed full of crazed cultists, daemonships created by the Dark Mechanicum, and other forces of the Lost and the Damned. None of these assaults reached Terra itself, but it was a rare week that the defensive cordon at the edge of the Sol system didn't have to destroy one of them and drag its wreckage out of the way for the shipments of food and supplies that constantly made their way to the Throneworld. When the ragged fleet of the Death Guard finally arrived, dragged from perdition by Mortarion's indomitable will, the defenders of Terra almost opened fire on them out of habit.

Then, after years of fighting such a long and gloryless war, the armies of the Traitor Legions and their allies finally arrived to the Sol system. The Sons of Horus, warned by the seers of the Thousand Sons and the agents of the Alpha Legion alike, had all returned to Terra, ready to die on the walls of the Imperial Palace in order to defeat the Arch-Traitor and restore the rightful rule of the Emperor over the galaxy.

The Siege of Terra : Victory Through Sacrifice

Though they took a heavy toll on the rebel forces by making Guilliman sacrifice an entire fleet to thin the veil and bring forth a daemonic armada, the outer defenses Perturabo had built in the Sol system were unable to stop the Traitor Legions. Both Horus and the Lord of Iron had known this to be inevitable, and they were prepared to fight both in orbit of Terra and on the Throneworld itself. The fleets of the Fourth and Sixteenth Legions, alongside the remnants of the Fourteenth and the Fifteenth and hundreds of loyal Imperial Navy vessels, fought against the traitor fleet in the skies of Terra.

For all their valour, however, they couldn't prevail against overwhelming numbers, and were eventually forced to withdraw, allowing the traitors to land. For the rest of the Siege, under the guidance of some of the greatest admirals the Imperium has ever known – such as Tybalt Marr "the Either", Captain of the Sons of Horus 18th Company – the loyalist fleet launched daring raids on the traitor fleet. In these assaults, the loyalists focused on inflicting as much damage as it could before retreating in the immensity of the void between the worlds of Sol.

And thus, the Siege began in earnest. With the Death Guard decimated at Isstvan V, the Iron Warriors having taken heavy losses in the Martian and Olympian Wars, and the Thousand Sons never having had a huge number of warriors, the Sons of Horus formed the bulk of the Space Marines who fought for the Emperor at the beginning of the Siege. Accounts of the Heresy who have survived the passage of time estimate that the Traitor Legions had a numerical advantage of at least five to one in Legionaries, however. Even with the additions Perturabo had made to the Imperial Palace and with the combined genius of two Primarchs leading the defenders while Mortarion fought on the front, it was doubtful they would be able to hold for long. Still, every man, woman and Astartes on the walls was ready to die before taking a single step back.

Then, moments after the traitors had landed, the odds suddenly changed dramatically. Guilliman, for all his planning and scheming, had failed to take into account the true nature of his allies, and they broke from his carefully designed battle-plan almost instantly. The Imperial Fists, who had claimed the honor of landing first, charged ahead, their hatred of Perturabo's sons driving them to crush the walls of the Palace themselves. Though Guilliman was able to retake control of the Seventh after their first assault was pushed back, the losses taken by the sons of Dorn had already thrown his plans in disarray. Then there were the White Scars and Space Wolves, those who had come to Terra, who completely ignored his instructions, mounting raids of their own and barely fighting alongside the other Traitor Legions.

But worst of all were the Blood Angels – an entire Legion that, in place of fighting to claim the Imperial Palace and seize victory for the rebellion, turned their attention on the defenceless population of Terra. Without the support of the sons of Sanguinius, Guilliman found that he couldn't breach the walls of the Imperial Palace, and though his forces and the loyalists' both took tremendous casualties with each passing day, his control over the other Traitor Legions frayed more as well. For several days, the defenders of the Palace believed that soon their foes would turn on each other. The knowledge Horus had gained of Chaos told him that such an event was inevitable. But before the nature of the traitors became their undoing, Lupercal's was his own.

From the command centre in the Imperial Palace, Horus saw the horrors perpetrated by the Ninth Legion, and his rage knew no bounds. After weeks of holding it back while directing the armies of the Imperium in defense of the Palace, his wrath finally became to much to hold. He left the command of the defenders to Perturabo and went to the Eternity Gate, where he slaughtered the attacking Traitor Marines by the dozen. All the while, he shouted for his brother to show himself, to come and confront him, that he might face justice for his crimes.

High in orbit, trapped in the veil of madness that had descended upon him at Isstvan, Sanguinius heard the call of his brother, and returned to his senses. Driven by grief and guilt, he descended to face Horus, his mind torn between his desire to protect his sons and his horror at what they had become. The two Primarchs fought, and Horus claimed the upper hand. Sanguinius was brought low and laid at Horus' mercy, but just as the Warmaster was about to deliver the killing blow, he hesitated. Lupercal looked into his brother's eyes and saw not the monster he had become, but the Angel he had once been. That second of hesitation was fatal, for Sanguinius' soul broke in that moment, and Slaanesh consumed him wholly. The fallen Angel rose and drained Horus of his lifeblood, transforming into a Daemon Primarch in the process.

'Brother ... What have they done to you ?'
Last words of Horus Lupercal, First Warmaster of the Imperium (allegedly)

The death of Horus was a terrible blow to the Imperial defenders, but even more so to his Legion. Perturabo had to exert all of his will to keep the Sons of Horus from charging recklessly into the enemy ranks, so strong was their urge for revenge. It is said Ezekyle Abaddon and Tarik Torgaddon had to be physically restrained by the rest of the Mournival. Despair threatened to overcome the defenders, for with the fall of Horus had also come the sudden return of the Blood Angels from their butchery and into the fray. Then a vox transmission echoed across all of the Terra, coming from the Legion flagship Andronicus : the Emperor's Children, lost during the Heresy and thought to have been destroyed, had arrived. Immediately after came another transmission, this one from Sevatar, Legion Master of the Night Lords.

Horus was dead.

The thought was impossible. It couldn't be true. But it was; they had all seen it. They had seen their father falling to the one he had called brother, the one he had loved most. From up the walls of the Imperial Palace, they, like all other warriors – loyalists and traitors alike – had frozen and watched the moment the Warmaster had died.

Ezekyle and Tarik were enraged. Their screams were shaking the very stones of the Imperial Palace. But even as he held them back, with the help of Aximand and other warriors, Gavriel could hear the other emotion in his brothers' voices. Like him, they were being torn apart inside.

'You can't go there, Ezekyle !' he shouted, trying to make his brother see reason. 'He will kill you !'

'I don't care ! He killed our father ! He must die ! He must … He must …'

The words stopped even as the First Captain ceased to struggle. Terminator armor wasn't designed to allow much freedom of movement, but Gavriel was fairly certain that had his brother worn a traditional suit of power armor, he would be on his knees. Ezekyle Abaddon, who had fought the enemies of the Emperor on a thousand worlds, who had gone through the entire civil war with the same expression of contained fury on his face, was weeping like a child.

And Gavriel knew that tears were running down his own face. He didn't care. Horus was dead. There was no hope …

And then, they heard it. A change in the vox transmissions. A difference in tone, at first so minute anyone with less experience than them wouldn't have noticed it. Something had happened that was changing the course of the battle. A new transmission started to register in their vox-systems, and for a moment Gavriel couldn't believe the identifier on it. It was a code he had seen during the Great Crusade's early days, before Nikaea, before Ullanor, when the Luna Wolves had fought alongside another Legion.

'Fulgrim ? …' he breathed, unable to comprehend what he was seeing. No one had heard of the Third Legion since the beginning of the war. A hundred rumors circulated about the fate of the Emperor's Children – some thought they had been destroyed by the traitors, others that they had joined them and were being held as a reserve force. For a second, Gavriel was at once relieved to hear that the Phoenician lived, and horrified that maybe this indicated the arrival of traitor reinforcements.

Then the words reached the grieving Mournival, their pronunciation rough, as if the one speaking them was doing so through grievous injuries.

"In endless agony reborn ..."

"By the blades of true brothers returned ..."

"Enemies of the Emperor, we have come for you !"

In orbit and on the ground, the two Legions unleashed all of their might against the Traitors. The members of the Mournival, now in command of the Sixteenth Legion, seized the opportunity. As they ran through the Imperial Palace, they communicated with the leaders of the two newly arrived Legions, forming a plan that was as bold as it was desperate. While the Night Lords prevented the arrival of enemy reinforcements, the Mournival, together with their four Companies, would attack the Eternity Gate. The four warriors at the head of this assault, each a legend of the Great Crusade in their own right, were determined to slay the vile traitor Sanguinius and reclaim their father's body.

They were dying. Worse : they were losing.

What had begun as a glorious counter-charge against the tide of darkness had turned into a desperate struggle for survival. In his mind, Ezekyle Abaddon knew that this was to be expected. No matter what he had become, Sanguinius still possessed the might of a Primarch, and no mere Legionary could challenge such power. But his heart ... his heart felt very differently. His heart burned with the thirst for righteous revenge, sorrow at his father's demise, and a primal, animal need to help his comrades.

"Little Horus" Aximand was on the ground, his guts torn open, half his face torn away by the blade of the Traitor Primarch. Tarik had lost his left arm, but he still fought, back to back with Gavriel – brave, stalwart Gavriel – even as they both bled from a dozen wounds.

And what was he doing, he the First Captain, he whose battle-rage and martial skills were legendary across the Imperium ? He was dragging himself on the ground like a worm, inch by inch, toward the corpse of his father. He didn't know where the idea had come from, and yet he knew that there was only one way for them to kill the monster Sanguinius had become. With hands that trembled both because of the pain wrecking his body and that burning in his soul, Abaddon detached the great Talon from his father's hand, and slid it upon his own.

It shouldn't have worked. For all the simplicity of its use, the brutal elegance of its design, the Talon was still a weapon of war that had been forged by the Fabricator-General of Mars himself as a gift to Horus. It should have taken half a dozen tech-priests several hours of rites and calibrations to adapt it to Abaddon's Terminator war-plate, to link between the weapon's machine-spirit and that of the armor. And yet ...

The moment the Talon of Horus slammed into place around Ezekyle's hand, the lightning claw roared into life, power coursing through each blade. The First Captain thought he could feel the weapon's rage, its desire to avenge its fallen master just as great as his own. Abaddon felt a surge of strength through his battered and bruised body, and leapt to his feet before charging with far more speed than he had ever displayed.

'Lupercal !' he shouted, his cry both of challenge and mourning, a lamentation of what had already been lost and a scream of defiance to the dark powers that had created the abomination he faced.

Five claws pierced the chest of the fallen Angel, and burst out of the creature's back in a shower of blood. Yet still the daemon remained standing, staring at Abaddon with eyes filled with madness, a demented grin on his once-beautiful features.

Then the head exploded as Aximand, still spilling his guts on sacred ground and with half his face a bloody ruin, rammed Worldbreaker into it. A horrible, inhuman shriek resonated across the entire surface of Terra as the fell spirit Sanguinius had become lost its grasp on the material plane and was hurled back into the infernal aether.

But this victory was short-lived. Warriors clad in the blue of the accursed Thirteenth joined the battle even as most Blood Angels fell to the ground in agony. The members of the Mournival, wounded and exhausted, stood their ground, but to their horror, they found themselves separated from Horus' corpse. That horror only grew when they saw some of the Blood Angels approach that body, and start dragging him away.

'Give him back !' roared Gavriel, tearing through the ranks of the Ultramarines as he tried to advance, to kill the wretches who dared to touch his father's body. All thoughts of restraint, of tactics, had deserted him, replaced by the all-consuming need to protect his Primarch's corpse, to not fail him in death as he had failed him in life. 'GIVE HIM BACK !'

Against all odds, the four warriors destroyed Sanguinius' corporeal form, banishing his spirit back to the Warp. But even as they claimed this mighty victory, traitor reinforcements arrived in the form of several companies of Ultramarines, sent by their foul master to capitalize on Sanguinius' presence on the front line. The Traitor Marines kept the Mournival away from Horus' body, and it was all the Sons of Horus could do to watch in horror as the Blood Angels withdrew from the field, carrying with them the corpse of the First Primarch.

Many among the Sons of Horus wanted to charge down the walls of the Imperial Palace in order to reclaim their gene-sire's remains, but even if they had been ready to break their sacred oaths, they would have been hard pressed. Guilliman had reacted to the arrival of the Third and Eighth Legions as well, and had launched one last attack on the Palace, led by himself and his brothers in damnation.

The walls of the Imperial Palace were breached, and Guilliman, Lion El'Jonson and Rogal Dorn entered the Cavea Ferrum, while the Sons of Horus and their allies desperately fought against Ferrus Manus and his twisted Marines holding the gate. Many heroes of the loyal Legions fell that day, until word came from the depths of the Imperial Palace : Roboute Guilliman, the Arch-Traitor, was dead. The Traitor Legions broke and fled, their backs exposed to the Sons of Horus, who did not hesitate a second to open fire.

Soon, the ships of the traitors had either fled or been destroyed. The Heresy was over, and the Imperium had triumphed, at the cost of its founder and its bravest and most noble sons and daughters.

Post-Heresy : A Stained Honor

'I was there, the day the Great Crusade ended.
I was there, the day Horus died for the Emperor.
I was there, the day the Emperor died for Mankind.
I was there, the day the Black Legion was born.
And I will be there the day it dies.'
Unknown warrior of the Sixteenth Legion (generally attributed to Garviel Loken)

Though the Emperor had defeated Guilliman with the help of Fulgrim, the Master of Mankind had been terribly wounded in the battle, and had to be sat upon the Golden Throne to preserve even the smallest flicker of His life. So it was that the Sons of Horus, having already lost their gene-sire and commander to the ravenous claws of Chaos, also lost their liege lord to eternal silence.

Amidst the confusion that followed the flight of the Traitor Legions and the arrival of the Twelfth and Seventeenth Legions, it fell to the members of the Mournival to hold the Imperium together. With the Emperor silent and Malcador the Sigillite dead, the possibility of the Imperium collapsing was entirely too likely. It was the combined efforts of the four warlords who kept this downfall at bay, for together, they held the same strengths and skills as their lost father.

With the aid of the remaining Primarchs, these Mournival Lords, as the grateful population of Terra soon named them, brought the Imperium back from the brink. From the survivors of the Heresy, they named new Lords of Terra to replace those who had fallen. In an act that helped seal the authority of this new Council, they bowed to the decision that no Primarch or Astartes would hold authority over the Imperial Army, to prevent such an event as the Heresy from happening again. The title of Warmaster, bestowed by the Emperor upon Horus, was also stripped of much of its power, becoming a rank the High Lords would grant to the greatest generals only in time of dire need, and for a limited period.

So did the Imperium begin to rebuild itself after the horrors of civil war. But the darkness unleashed by Guilliman was far from banished : though they had fled from Terra, the Traitor Legions still haunted the galaxy. Once the Lords of Terra were firmly in control of the Throneworld and the nearby systems, the Sons of Horus prepared to join in the effort to scour the traitors from the stars. Together with the entire force of their Legion, the four Mournival Lords waged terrible war upon the enemies of the Throne. On a thousand worlds, the sons of Lupercal fought against traitors from all Legions and their allies, both human and daemonic. The rage and sorrow they felt for the death of their father, for the loss of the Emperor, for the doom of the Imperial Truth, was finally unleashed. The wolves of Chthonia mourned their liege in a manner befitting their kin : by making pyres of their enemies' broken corpses.

Yet for all their fury, the Sons of Horus weren't invincible. The Scouring inflicted grave losses on the Legion, and by the time the last of the traitor warbands was either destroyed or cast behind the walls of the Iron Cages, less than ten thousand Legionaires remained who wore the Eye of Horus. Two members of the Mournival had also fallen, their deaths remembered and honored in every sanctuary of the Sixteenth Legion.

Tarik Torgaddon, Captain of the Second Company, fell in battle against the Daemon Prince Samus. The creature had already been defeated several times during the Heresy, but it had always found a way to return to the Materium. Tarik, however, managed to inflict such damage upon the lord of the Immaterium that it still has to reappear today, after ten thousand years of banishment.

'Samus is here,' growled the beast, bending its head so that it could look down upon the battered, lone warrior who faced it.

Tarik laughed, and the creature roared in fury at his mockery – or perhaps it was fear. In his hands, the son of Horus held Worldbreaker, the weapon that had killed a Primarch. He had been the one to receive it after Lupercal had fallen – Aximand, though he had used it against accursed Sanguinius, had refused it. Did the beast recognize the weapon, Tarik wondered ? Did it fear it, more so than the warrior that wielded it ?

If so, then it was a fool.

'Samus is here !' it bellowed, raising its weapon, a hideous thing of black metal and twisted angles.

'Not for long he isn't,' Tarik promised, and charged the Daemon Prince, his Primarch's power maul held high.

The second of the Mournival Lords to fall during the Scouring was Horus Aximand. The Captain of the Fifth Company lost in life in a duel against Sigismund of the Imperial Fists. Aximand's forces – made of Sons of Horus, but also Imperial Navy and Mechanicum ships – had found the Seventh Legion as it fled toward the Eye of Terror. But just as they were ready to wipe the foul sons of Dorn and their Primarch from the galaxy, Sigismund launched a daring attack on Aximand's command ship, disturbing the formation of Imperial forces and giving his Legion an opening to escape. Aximand fell by the blade of the champion of Khorne, but in what was either an insult or a sign of respect, the Destroyer left the body intact instead of taking his skull.

'You fought well,' said Sigismund as he pulled his blade from Aximand's chest. The daemon weapon, forged in the fires of the Blood Crusade, pulsed with hunger as it sought to devour the soul of its victim, only to find it too strong.

His two hearts had been pierced, blood was gushing from the wound, yet somehow the Mournival Lord remained standing. His face, regrown and reattached after his fight with Sanguinius, stared at the Imperial Fist before him like that of an ancient king rendering judgement upon a criminal, and Sigismund felt the vestige of something akin to fear – or was it shame ? – inside him. Without a word, his sword, the blade Mourn-it-all, came down upon Sigismund's own hastily raised blade, and the two weapons shattered under the strength of the impact, sending both Aximand and Sigismund flying across the ravaged bridge. Aximand's corpse hit the wall and slid to the floor, while Sigismund was engulfed in a twirling maelstrom of Warp energy and, with one last scream, was taken from the material plane by the rage of the unleashed daemon.

With the Scouring complete, the Sons of Horus returned to their various strongholds, to heal their wounds, repair their ships, mourn their brothers and replace their casualties. There was peace in the Imperium, though the Imperial Truth had been forever broken, and faith and superstition were rising in its place. Several decades passed, which the Sons of Horus spent rebuilding what they had lost. Then, a hundred years after the battle of Terra, an astropathic message from the Iron Cage around the Eye of Terror reached the Legion's headquarters in the orbit of Chthonia.

Cadia had fallen to the Ninth Legion, the message said. That alone was bad news enough, for the fortress-world had been one of the best defended of the Iron Cage, and the linchpin of the Iron Warriors' efforts to keep the Traitor Legions contained. Yet even worse was the rest of the message, which spoke of malformed clones fighting alongside the Blood Angels, whose traits uncannily resembled those of the dead Warmaster – and whose gene-seed their dissected bodies had revealed they shared. Another traitor had been sighted as well : Fabius Bile, once the first Apothecary of the Third Legion, who had disappeared during the Bleeding Wars and had been presumed dead. The abominations fought under his banner, and he also appeared to be in relative control of the Blood Angels. The first of the Black Crusade had begun, and the Imperium's armies must be raised to fight and cast the traitors back into their infernal prison.

The piece of information that set the Sons of Horus on the warpath, however, was the fact that several witnesses claimed to have seen the body of Horus Lupercal being brought to Cadia and into one of the laboratories built at Fabius' command. After relaying the message to the Emperor's Children and demanding that Fulgrim explains the actions of his son, the full might of the Sixteenth Legion departed for the border of the war zone, where it joined with the Iron Warriors and the Emperor's Children. With the first, devastating counter-attack led by the Mournival Lords themselves, the Clone Wars began.

The traitor forces under Bile's command had claimed dozens of system during the initial push, only to settle down as their master began to use the captured population and Legionaries for his unholy experiments. Reclaiming these worlds and purging them of heresy would be a task that would last for many years, but from the moment the Sons of Horus fought against the creations of Bile for the first time, their sole focus became the destruction of the Primogenitor and his foul get.

Misshapen Astartes, hideous abominations of flesh, and hordes of cloned mutants had been unleashed by Fabius Bile, under the leadership of the greatest horrors of all : the clones of Horus who were complete success, but were then twisted by the dark powers of Chaos. These warlords commanded the armies created by their Primogenitor, and called themselves the Black Legion – a malevolent reflection of the twenty Space Marine Legions created by the Emperor at the dawn of the Great Crusade. In daemon ships forged in the Eye of Terror by the Dark Mechanicum, they rampaged across the territory conquered by the Black Crusade, and the Sons of Horus vowed to bring every such abomination down, no matter the cost.

The Black Legion

Of all the warbands and gatherings of traitors and heretics, the Black Legion is the most foul, and perhaps the most powerful. Born from the spawn of Fabius Bile's failed experiments, its strength has waxed and waned over the ages, yet never has it been completely eradicated – and Imperial strategists fear that such a feat is impossible. Their banner of the Eightfold Star of Chaos Undivided has been raised on battlefields across the breadth and width of the entire galaxy, against all manners of enemies – though most often against the forces of the Imperium. None of the four Chaos Gods are especially favored by its members, though individuals within its ranks do walk the Path to Glory, with several having reached its ignominious end and been reborn as Daemon Princes.

Any warband can claim affiliation to the Black Legion, and over the years Legionaries from all nine Traitor Legions have cast aside their former allegiance have "donned the black". Even renegade groups made up entirely of humans and mutants can decide to bear its foul emblem as their own, though more powerful warbands might be insulted by such presumption. Other Traitor Legions regard these groups as fools and inferiors, and have often attacked them for slaves, supplies, or sport. Yet even these ancient warlords know, deep within their tortured souls, that while their own Legions grow weaker with the passing of time and the death of their warriors, the Black Legion only gets more powerful with each century.

While Fabius Bile is revered as the Primogenitor of the Black Legion, he has little interest in actually leading it to war. Like the Traitor Legions, the Black Legion is divided in hundreds of warbands with individual leaders, and it is far from uncommon for these warbands to fight one another. But the name of the Black Legion has spread far and wide, and whenever Astartes from the loyal Legions succumb to the lures of Chaos and break their oath to the Imperium, it is often to the Black Legion they turn. This, combined with the products of Bile's ongoing experiments always joining the horde, has kept the Black Legion's numbers high since the end of the Clone Wars. Should any warlord manage to rise to truly unite it, or Bile take a greater interest in his errant children, the Black Legion would be a terrible threat not just to the Imperium, but to all life in the galaxy.

For several years, the Sons of Horus fought to purge the Imperium from the taint of the Black Legion and the Blood Angels. With the help of the Iron Warriors and the Emperor's Children, they managed to push back the forces of Chaos, until eventually the warriors of the Ninth Legion were recalled in the Eye of Terror – the War of Woe had begun, and Azkaellon needed every warrior to oppose the Imperial Fists.

This allowed the Imperial forces to launch one final attack, directly onto the invaders' primary fortress. There were the cloning facilities from which the monsters of the Black Legion were spawned, there laid the desecrated corpse of Horus Lupercal – there was the Primogenitor. While the Iron Warriors fought in orbit against the Chaotic fleet, the Emperor's Children and the Sons of Horus descended upon the planet to purge it of evil. After much discussion, it had been decided that the Sixteenth Legion would destroy the cloning facilities and reclaim their father's body, while Fulgrim himself would hunt down his wayward son and bring him to justice.

The battle of the Clone Pits was gruelling and nightmarish, with the Sons of Horus facing countless abominations. Ezekyle Abaddon, Mournival Lord and hero of the Great Crusade, was separated from his forces, and brought low by no less than three of the horrendous clones of his Primarch – though he killed them all in return. In the end, it was Gavriel Loken who reclaimed Horus' body, and later ordered it burned so that it could never again be used against the Imperium in such a manner. The cloning labs burned with their progeny, but Bile escaped judgement, unleashing a horde of malformed clones of Fulgrim upon his Primarch to slow him down while he cowardly escaped. The Clone Wars were won, but many of the creations of the Primogenitor escaped, and they would haunt the Imperium for millenia to come.

'Lupercal !' Abaddon howled as he plunged the Talon into the chest of another clone. The four blades burst out of its back in a shower of blood, and the abomination fell.

But there were still two more, and Ezekyle was bleeding from a dozen grievous wounds. The assault on the cloning facilities had not been easy, and he had gotten separated from the rest of the Justaerin.

My own damn fault, he thought as he turned to face the remaining clones. If I hadn't charged ahead …

He shook his head. Regrets meant nothing now. Whatever happened to him, Gavriel would take care of things. He would make sure this place was burned to the ground. Some part of Abaddon wondered if perhaps he had deliberately pushed forward, ahead of his men. Perhaps he couldn't bear it any longer – they had lost so much. The faces of lost brothers haunted Abaddon's nights, driving him to ever greater feats of endurance and martial skill to avenge their spirits.

'I will see you soon, brothers, father,' he whispered, before forcing his burning muscles into motion once more, determined to meet the last abominations head on.

'Lupercal !' he roared as their blades pierced his hearts, and the Talon cut through their armor and into their corrupted flesh.

At some point, either during the end of the Clone Wars or soon after, Garviel Loken, the last of the Mournival Lords to have held his position since the Heresy, vanished. Not even in the Ordos' most secretive archives can any clue as to his ultimate fate be found, safe for a single quote that is believed to come from him and that predicts his presence on the day the Black Legion is finally destroyed. The Sons of Horus believe him dead, and honor him in the same way as the other three first Mournival Lords.

The end of the Clone Wars marked the definitive transition for the Sixteenth Legion from the Heresy into the Age of Imperium. The Sons of Horus scattered across the Imperium and started to wage the countless wars that would be required for Mankind to survive. Always they are at the forefront of any expansion effort, thriving on the same spirit of conquest that inhabited them during the Great Crusade. But even then, the echoes of their past have never truly left them. Hundreds of champions of the Sixteenth Legion have left their brothers over the millenia to go on hunting quests, vowing to bring the Arch-Renegade Bile to justice. Though several of them have claimed to have slain the betrayer, each time they have been proven wrong as the Primogenitor reappeared, leading another raid in realspace or having dealings with rebellions and cults across the entire galaxy. The reason for that apparent immortality is unknown, though there are several theories in both the Sixteenth Legion and the Inquisition, ranging from dark pacts with powerful daemons to the most blasphemous of genetic perversions.

During the thirty-eight millennium, the animosity between Fabius Bile and the Sons of Horus escalated to yet another level as the foul Primogenitor unleashed one of his most cruel and twisted plans ever. The exact details, as well as the names of those who were involved, are kept secret by the Sixteenth, who only revealed what the Inquisition does know grudgingly, unwilling to add another inglorious passage to their history.

Bile, after millennia of being opposed by the Sons of Horus, had designed a scheme that he believed could destroy the Sixteenth Legion forever. In his gene-laboratories of the Eye of Terror, he created a young man that, to any human and even psychic eye, appeared to be completely normal. This creature was then taken by his agents to one of the Sons of Horus' recruiting worlds, and introduced into the local population. The clone himself knew nothing of his origins, his mind shrouded by implanted false memories that convinced him that he had always lived on the planet.

When the Sons of Horus came to bring new recruits to their Apothecaries, the young man was immediately singled out, for he had demonstrated incredible strength, endurance, but also courage, honor and leadership. He was taken into the ranks of the aspirants, and even the most careful screenings of the Legion Apothecaries failed to discover his true nature. He did incredibly well in training, and soon received the implants that made him first a Scout, then a true Legionary.

Bile had designed his creation with all the evil genius he had become infamous for, and the introduction of the Sixteenth Legion's gene-seed reacted with the secrets he had implanted within his pawn's gene-code. The clone grew in strength and stature like all of his comrades, but his own growth didn't stop at the level of a normal Space Marine, and continued until he was of the same size as the legendary Primarchs of old. Those around him believed him to be blessed by the Emperor, his transformation a result of a particular affinity with Horus' gene-seed. This strength, combined with undeniable martial qualities, led to the unknowing plant becoming Captain of an entire Company. Many enemies of the Emperor were brought low by his hand, but then, Bile's plan entered its second phase.

Visions of the Great Crusade and the Heresy started to haunt the clone. Slowly, without realizing what was happening to him, he came to believe that he was Horus Lupercal himself, reborn in the flesh after ten thousand years. Many Sons of Horus also believed in this reincarnation, such was the likeness of the clone, both in appearance, but also in martial skill and behaviour. He matched the First Warmaster described in the archives perfectly, and the Sons had ever longed to be reunited with their lost father.

Pushed along by the manipulations of secret agents of Bile, the self-proclaimed Primarch tried to seize control of the entire Legion, as he genuinely believed was his right and duty. He called the Mournival Lords to him, that they may bend knee and rejoice at the reunion. The four lords answered his call, but not to kneel. They had inherited the accumulated knowledge of their predecessors, including secrets that had been kept from the rest of the Legion. They knew the true extant of Fabius Bile's hideous work during the Clone Wars.

With ranks of Legionaries facing each other in tense silence, the Mournival Lords confronted the clone. They decried him as a fraud and a heretic, naming him the False King. They vowed to see him destroyed, and the Legion freed from the lies he had, willingly or not, brought with him. This event is recorded in the Ordos' archives as the Denunciation of the False King, and while it was right that the clone be exposed as the abomination that he was, there would be dire consequences to the Mournival's decree.

'Horus was the greatest of the Primarchs. He was our father, in blood and in spirit. Under his command, I would venture into the Eye of Terror itself and spit in the face of the Dark Gods. But you are not him. You are a lie, clad in flesh born of our great enemy's mad genius. Horus is dead, and can never return !'
From a member of the Mournival, during the Denunciation of the False King

What followed was a bloody and terrible civil war within the ranks of the Sixteenth Legion. The False King, during his rise, had accumulated millions of mortal soldiers to his cause : they had flocked to him, blinded by his greatness. Now they died under the might of the Sons of Horus, in a campain that lasted for three months and reduced several once-mighty worlds to ruin. Thousands of Legionaries on both sides died, though several Companies whose leaders had been deceived by the False King returned to the fold after some among their ranks rose against the treachery of their masters.

As the conflict dragged on, signs began to appear that confirmed the words of the Mournival Lords. Warbands of the Black Legion started to take part in battles, fighting against the Sons of Horus unaligned with the False King and retreating rather than fight the others. Some of the warriors fighting under the banner of the one they believed to be Horus Reborn started to suffer from mutations, their Librarians driven to insanity and corruption by the laughter of daemons.

The War of the False King, as it came to be known, ended with the death of the cloned Primarch. By that point, the warriors that were still loyal to him were little different from Chaos Marines themselves, drenched in corruption and self-delusion. When the forces of the Imperium finally cornered him in his final fortress, his genetic make-up had begun to decay. He was afflicted with mutation and madness, at long last realizing the truth of his nature. It is said that he welcomed the blade that ended his life and freed him from an existence of lies. Every trace of his deeds before his rebellion were erased from the Legion's archives, and his very name was destroyed, to the point not even the Mournival Lords know him by anything but the title they gave him during the Denunciation.

'Brother … I am sorry …'
Last words of the False King (unverified)

The Inquisition thoroughly investigated the warriors who had initially followed the False King but turned their back on him later. They willingly submitted themselves to these examinations, wanting to purge the shame of their deeds in any way necessary. A few of the False King men, however, survived and escaped, most of them joining the ranks of the Black Legion. It is said that they hope the Primogenitor will give them another Primarch to lead them, and are willing to perform any deed, no matter how vile, to earn this gift.

A thousand years after that terrible affair, yet another blow was dealt to the Sixteenth Legion, though it came with what the Imperium at large considered a boon. In the year 392 of the forty-first millennium, Lord Commander Solar Macharius was named Warmaster by the Senatorum Imperialis, and declared a Crusade to expand the domains of the God-Emperor to the confines of the galaxy. He led a massive army to the Imperial frontier in the Segmentum Pacificus, the likes of which had not been seen since the days of the Great Crusade.

The Sons of Horus had always supported those deemed worthy of the title of Warmaster, especially when they attempted to push the boundaries of the Imperium further. A full third of the Sixteenth Legion joined the Macharian Crusade, with two members of the Mournival leading them and counting among Macharius' favored advisers. As per the tradition of the Sixteenth, one of the Mournival Lords sent was calm and collected, while the other carried with him the passion of the Legion, that the two might balance each other.

However, the Mournival Lord tasked with keeping both his brother's and Macharius' own drive for conquest fell in battle early in the Crusade. In the Karsk system, the forces of the Imperium met their first true challenge in the form of the Cult of the Angel of Fire, debased humans who worshiped a Lord of Change – the titular Angel. The Greater Daemon killed the Mournival Lord, only to be defeated and banished moments later by Macharius himself, whose soul was able to resist the false promises of the daemon and hold to faith in the God-Emperor.

Despite the ultimate victory, the death of the Mournival Lord would have lasting consequences for the Crusade. The ambitions of the Warmaster and the remaining Space Marine commander fuelled each other, and the Crusade advanced at a prodigious pace, claiming a thousand worlds in only seven years. The Sons of Horus spearheaded the assaults, while Macharius' tactical genius allowed him to turn these initial gains into strongholds. As the year 399.M41 neared a close, the forces of the Imperium were approaching the galactic border, beyond which there laid only the cold blackness of the abyss, far from the light of the Astronomican.

At this point, even the remaining Mournival Lord counselled Macharius to end the Crusade, content in the knowledge that they had brought a thousand worlds into the Imperium. But Macharius wanted more. He wanted to push on into the Halo Zone, to let nothing escape his conquering grasp. However, when faced with the opposition of the Sons of Horus, but also of most of his own generals and other advisers, he relented. His forces were delighted to know that the Crusade was over, and prepared to return to Terra in glory.

On the way to the Throneworld, however, tragedy struck, and Macharius died. The exact circumstances of his demise are unknown. Official records indicate that the Warmaster had contracted a potent fever on one of the worlds he had conquered, and the disease had finally taken him. Yet there are many other versions in the Ordos' archives : some claim that Macharius, broken by the refusal of his men to continue the Crusade, simply faded away in his sleep or even took his own life. Other accounts tell of darker reasons for his death, which, if confirmed, would shed a disturbing light on the events that followed it.

The human who dared to claim the title of Warmaster looked upon Azrael with hate-filled eyes, but no sound passed his lips. The agents of the Lord of Lies had worked well, poisoning Macharius over the course of the entire Crusade, all so that when the end came, his soul would belong to Azrael.

It had truly been a master stroke, the Dark Angel reflected, one that would soon result in destruction untold across the Imperium. The brutish Sons of Horus hadn't even realised they were being manipulated by the scions of the Great Changer. With Macharius' soul in his grasp, Azrael would be able to do as he pleased with the body, and the triumphant Warmaster would rise against the Lords of Terra, causing a civil war the likes of which had not been seen since the days of the Heresy. His generals, carefully groomed over the course of several generations, would follow him – their ambition would allow no other outcome.

He reached out with his mind, preparing to tear the essence of the great general from his body. But to his initial surprise and growing horror, he found that he couldn't touch it. Something was protecting Macharius' soul from his grasp, and the life of the Warmaster was fleeing. In mere seconds, he would be dead, and it would all have been for nothing …

'For the Emperor', said a voice behind Azrael, and the Grand Master had just enough time to turn around before a bolt shell crashed through his chest plate and into his primary heart. Before his enchantments took him away and back to the First Legion's homeworld – where he would have to explain his failure to his Primarch – Azrael caught a glimpse of a transhuman silhouette in green, scaled armor …

The Sons of Horus honored the death of their ally, and prepared to leave the territory claimed by the Crusade, leaving it in the hands of Macharius' human generals so that it might be added to the Imperium proper. However, no sooner had the Warmaster breathed his last that the seven generals who had led his Army Groups turned against each other and the Imperium. They divided the territory conquered by the Crusade into petty empires and crowned themselves lords. So began the Macharian Heresy, named after one of the two warlords who failed to notice the growing ambitions and blackening souls of those under their command.

Obviously, the Sons of Horus were outraged by such base treachery. For thirty years, they scoured the Segmentum Pacificus, hunting down each of the treacherous generals and killing him within his most secure stronghold, showing to those who had foolishly followed his command into rebellion the price of betrayal. Chaos forces began to appear in the war, allying themselves with the rebel generals or taking advantage of the destruction to plunder and despoil. A warband calling itself the Minotaurs, believed to be an off-shot of the Thirteenth Legion, was notably responsible for the destruction of three entire worlds before the Sons of Horus cornered them in the Euxine system. Several of the generals also made direct pacts with the Ruinous Powers, sacrificing their traitorous souls to prolong their unworthy existences.

By the time the Sixteenth Legion's forces and the Imperial troops who had remained loyal were done, the swathes of space Macharius had conquered was in ruins. Only a small human population remained, and most of its existing industry had been destroyed. Still, the Imperium had gained a thousand worlds, to be colonized and exploited by the teeming masses of Mankind. To the High Lords of Terra, this was an acceptable result. Macharius was named a Saint of the Imperium by the Ecclesiarchy, his story used to inspire loyalty and devotion across the entire galaxy.

At the end of the Macharian Heresy, the Mournival Lord who had survived returned to the rest of his Legion in shame that he had failed to foresee the generals' betrayal. A new Mournival Lord was selected, and the brotherhood renewed its ancient oaths to preserve balance within its ranks, no matter the circumstances. So did the fifth century of the forty-first millenium began for the Sixteenth Legion with one more shame added to their past, and many more vows to atone for it through battle.

Now, as the forty-first millennium draws to a close, the forces of the Black Legion are rising once more. Dozens of warbands have been sighted outside the Eye of Terror, and more and more Chaos Marines from other Legions don the black of Fabius' armada with each passing year. All they await is a suitable leader, one willing to guide them out of the Eye and into war against the Imperium. Should such a Chaos Lord arise, he would be able to command a Black Crusade of unprecedented might – but would also find the full strength of the Sons of Horus arrayed against him, as the heirs of Lupercal seize the chance to finally erase the insult on their honor that is the Black Legion.

Lufgt Huron, the Savior of Badab

Born on the hive-world Badab Primaris, in the Segmentum Ultima, Lufgt Huron was selected to become a Son of Horus after the Twelfth Company of the Sixteenth Legion took heavy losses fighting back a massive pirate invasion from the nearby Maelstrom. Lufgt took well to the implants, and became a member of the Scouts. Only a few years later, during the conquest of the Eldar Exodite world of Lylogir, Lufgt distinguished himself when he killed a xenos warlock with his bare hands, resisting the witch's psychic assault through sheer force of will. Many among the Company believed this marked him for greatness, and he was quickly elevated to the rank of full Astartes.

Over the next century, Lufgt Huron rose through the ranks by displaying the combination of martial skill and tactical genius only seen in a few of the Legion's captains. When the Twelfth Captain, Rovik Blake, fell in battle against an Ork Warboss, he was selected by his peers to succeed him. This ascension was as quick as it was unceremonious, for with the fall of Blake, the Orks had seized the momentum of the ongoing conflict between them and Imperial forces of the Maelstrom zone. A Waaagh emerged from the Warp storm, and converged on Badab Primaris, Lufgt's homeworld. Determined to prevent the planet's loss to the Great Beast, Huron planned a devastating counter-attack, aiming to kill the Warboss who had killed his predecessor and break the cohesion of the enemy horde. The resulting duel left Huron gravely injured, with almost half of his body needing to be replaced by cybernetic augmentations, but the plan worked. With the death of their leader, the Orks turned on each other, becoming easy prey for the Imperial forces. The grateful population of the hive-world bestowed upon Huron the title of Savior of Badab, and he has since led many operations against all enemies of Man.

There is now talk among the Legion that Lufgt is in line for the Mournival, should a seat free itself – each of the four Lords is always on the look-out for his own potential successors, for to rise to that rank means an acute awareness of the reality of war, and none believe themselves immortal. Many, including within the Inquisition, have great expectations for the Savior of Badab should he ascend to such a position. Yet others fear what it might portend, speaking of prophecies that allude to a dark destiny for Lufgt Huron.

Organization

'I pledge to honor the Imperium, the Emperor, and the Primarch. With my life, I shall guard the soul of the Legion against the darkness. I shall guide my brothers into eternal war, and give my blood so that Mankind might live. This I swear, upon the shadow of the moon.'
The oath of the Mournival Lords

Only Horus was worthy of leading the Sixteenth Legion. Such is the firm belief of the commanders of the Sons of Horus, and they have clung to it for ten thousand years. That is why, unlike other Legions whose Primarchs have fallen or gone missing, they do not have a Legion Master. Instead, the Sixteenth is led by the four Mournival Lords, heirs to the famous lords who counselled Lupercal during the Great Crusade and the Heresy. Back then, the Mournival was only an informal circle of four warriors counselling the Primarch and speaking with his voice, holding no special official authority – though in truth, they were considered by all who knew of their statut to be among the lords of the Great Crusade. With the death of the First Primarch, however, they have become the supreme commanding officers of the Legion, choosing on which battlefields the Sons of Horus deploy and interfacing with the rest of the Imperium.

The most important aspect of the Mournival, however, is that these four Lords must each incarnate an aspect of the Legion, so as to maintain balance within them. Chthonian rage must be balanced by the Warmaster's wisdom, and strength at arm must be tempered by diplomacy, and the drive to conquer kept in check by concern for Mankind. When that balance is broken, usually as the result of two or more of the Mournival Lords dying in quick succession, the Sons of Horus lose their way until it is restored. It was when the Mournival was made up uniquely of heirs to Horus' aggression that the Reign of Blood was allowed to happen, while the Sixteenth Legion fought too far from Terra to hear about the horrors of Vandire's rule.

When one of the Mournival Lords fall, the others gather, either in person or through astropathic projections – an art their Librarians have mastered over the centuries out of the necessity of the four being scattered across the galaxy. They then commune on the possible candidates, until they are all in agreement. Since such discussions more often than not occur at the speed of thought, it is rare for them to last longer than a single day. The new Mournival Lord will not know of his elevation until he receives an astropathic transmission to this effect. When the four gather together – generally once ever few decades – those who weren't present at the previous gathering renew the oaths they vowed in private after their elevation. They swear to uphold the values of the Imperium, to honor the memory of the First Warmaster and the Emperor, and to avenge the many wrongs that have been inflicted upon the Sixteenth Legion.

Apart from the Mournival's ascended role, the Sons of Horus have retained the organization they had during the Great Crusade. Each Company is made up of a variable number of warriors, from only a few dozens to almost thousand, depending on its available resources, the recent losses it has suffered, and the kind of warfare it specialize into. Each company has its own culture, inherited from Chthonian gangs and passed on through the generations. Companies rarely operate on their own, instead banding together as needed to face the current threat. In these gathering, if the Legion is operating alongside other Imperial forces, the Captains elect a representative among their number to go on the war council. Otherwise, they select a leader, through processes that can go from simple votes to a series of duels at first blood, depending on the circumstances, the traditions of the Companies involved, and the character of the Captains.

The Talon of Horus & Worldbreaker

The Sixteenth Legion has in its possession two relic weapons of immense power and significance, wielded by their Primarch in the dark days of the Roboutian Heresy and used by the first Mournival Lords to banish the Daemon Primarch Sanguinius. These weapons are passed from one Son of Horus to another, with the Mournival Lords responsible for choosing a new wielder when the previous one falls. While they often choose one of their own, it is by no means unheard of for someone outside their circle – even someone belonging to the rank-and-file – to be selected for this. To carry such a weapon is an immense honor, and one not bestowed lightly, for the enemies of Man are always targeting the users of these relics, seeking to steal them and desecrate them. Members of the Ninth Legion especially are known to react very violently to their presence, though only the strongest of them can even bear to get near the two weapons without the echoes of their Primarch's agony overwhelming them.

The Talon of Horus is a great lightning claw combined with a heavy bolter, crafted by the Fabricator-General Kelbor-Hal as a gift to commemorate Horus' rise to Warmaster. The machine-spirit of the Talon is a vicious thing, and any Librarian standing near it suffers from headaches as the aggression of the weapon touches them through the Warp. It is said that those gifted souls who look upon the blades can see the blood of Sanguinius, still dripping from the Talon as if it had just inflicted the wound. In battle, the Talon is a devastating weapon that can be used at range as well as in melee, and those who wear it often use its awesome firepower to support dangerous beheading strikes against enemy positions. Over the centuries, the Talon has claimed the lives of thousands of leaders of the enemies of the Imperium.

Worldbreaker, meanwhile, is a massive power maul, that only a Primarch can wield with anything approaching grace. Such is the weight and size of the weapon that it can only be used by a warrior in Terminator armor, and even then it is a clumsy affair, lacking the speed and skill an Astartes is used to with most weapons. Given to Horus by the Emperor Himself, Worldbreaker is said to have been forged by the Master of Mankind's own artisans on Terra. Those who wield the weapon are slowed by its mass, but when they do reach the enemy, they are all but unstoppable. The power maul can be used to destroy tanks and walkers, and infantry troops cannot hope to resist its touch. On several occasions, the power field of the weapon has been known to pierce through the shields of small Traitor and xenos Titans, shattering their legs and bringing them down. Worldbreaker's machine-spirit also echoes with the blow that banished Sanguinius, and is the bane of any daemon that crosses its path. According to the records of the Sixteenth Legion and the Ordo Malleus, any Neverborn defeated by the power maul needs far longer to recover from banishment than when a more mundane weapon is responsible for its destruction.

Combat doctrine

'Cut the serpent's head, and the body will die.
One does not need to strike first to win – only to be the last to strike at all.'
Extract from a tactical lesson given to the Sixteenth Legion's aspirants

While the Imperium at large has dedicated its military might to the defense of its territories, the Sons of Horus have remained conquerors at heart. They flock to the ranks of the Imperial Crusades, and even when fighting to help hold Imperial worlds, their tactics echo those they employed during the Great Crusade. They specialize in overwhelming strikes against enemy leadership, or at their strongest position. Either as the vanguard of a campaign or called upon to end a prolonged conflict, the presence of the Sixteenth Legion means that a bloody shock assault will soon arrive. Such strikes are often led by the Sixteenth Legion's Terminators, known as the Justaerin. Ever since the days of the Great Crusade, the Sons of Horus have had access to more suits of Terminator war-plates than the other Legions, due to their statut as the Warmaster's Legion.

The Justaerin, the Lost First Company

During the Great Crusade, the Justaerin were the Legion's Terminator Elite, gathered in the First Company under the leadership of Ezekyle Abaddon. When the First Captain died during the Clone Wars and the Legion began to scatter in several battle-groups, so did the Justaerin. Some of them attached themselves to the Mournival Lords, pledging their lives in their defense, while others joined other Companies and assumed the roles typically assigned to Terminators. The First Company effectively ceased to exist, with Abaddon as its last leader, hence the nickname of the whole order as "the Lost First Company".

Eventually, these warriors who had once fought under Abaddon all died, their suits of armor inherited by others in the Company they had pledged themselves to. But their traditions lived on, and over time, every Terminator bearing the Eye of Horus came to call himself a member of the Justaerin. Always fighting at the forefront of battle, these Terminators are great and terrible sights to behold, for they break enemy lines like a grenade breaks exposed flesh.

The Sons of Horus favor melee over all other forms of warfare, for it makes the most of their transhuman physique. There are few enemies in the galaxy that don't know fear when being charged by Astartes, and the mere shock of the Sixteenth Legion's sudden arrival, combined with their martial skill, is often enough to end a war before the foe even knows it has begun. For all the balance brought by the Mournival, the Sons of Horus aren't afraid of collateral damage, and will not hesitate to use overwhelming force against their target. Such a use of power far in excess of what is required is meant to break the enemy's will and ensure the Imperial forces following the Astartes' spear-point have no difficulties bringing the foe to compliance. But war isn't the only tool available to the Captains of the Sons of Horus.

Every officer of the Sixteenth Legion carries within him some shard of their lost Primarch's greatness : they can be shrewd tacticians, terrifying warriors, but also great diplomats. In the Age of Imperium, this last trait is most used when interacting with other organizations of the Imperium, be they stuck-up noble Generals from the Imperial Guards, secretive tech-priests of the Adeptus Mechanicus, or obtrusive bureaucrats of the Adeptus Administratum. Many of the Sons of Horus with a gift for diplomacy employ the method known across the Legion as "the Abaddon gambit" which involves going to any negotiation accompanied by a warrior as blunt as possible, who will make plain to the other party what they are risking by refusing the Legion's demands. Then the diplomat will interfere, proposing a more peaceful alternative, and appear all the more reasonable for it. This tactic is said to have been used by Horus himself with the Mournival, and it has served the Sixteenth well over the centuries.

Homeworld

While the homeworlds of other Legions have prospered under the guidance of their lords, Chthonia has remained a savage place, and most definitely qualifies as a feral world, despite the remnants of technology scattered on its surface. The skies and soil are polluted by the thousands of years of reckless exploitation, forming great rivers of toxic liquids and piles of debris the size of mountains. It is in this environment that the gangs fight one another over what little resources remain, in an endless cycle of violence that allows only for the strongest to survive and none to prosper.

The Sons of Horus do not interfere in the daily affairs of its gangs, only taking a hand when signs of Chaos corruption appear – in which case they brutally purge all those involved. From their orbital fortresses, they watch the gang wars, searching for those worthy of becoming Legionaries. Apothecaries wander the tunnels of the world, healing those wounded in battle if they consider that their bloodline will strengthen the gene-pool. The gangs have learned, after many years, to leave this white-armored giants alone, though there are a few tales of young boys who fought against one and were not only spared, but taken to the stars as a reward for their courage and skill.

The people of Chthonia are aware of the greater Imperium, though they lack any true understanding of its scope and might. They worship the Emperor as the Master of Mankind and the one responsible for the occasional supplies appearing in temples and caches across the labyrinthine complex of the underground. In truth, these supplies are delivered by the Sons of Horus, to keep the cycle of life going on a planet where agriculture is all but impossible and food, air and water are recycled over and over again by ancient machines most Chthonian lack the knowledge to maintain and repair. Without these shipments, Chthonia's society, such as it is, would have utterly collapsed long ago in a vicious cycle as resources became ever more scarce and violence between gangs increased due to desperation.

Beliefs

'The Legion is all.'
Sixteenth Legion's motto.

To be Son of Horus is to be heir to the Imperium's greatest glories and greatest shames. They are the mightiest of the loyal Space Marines Legions, their victories are beyond counting, and they are the very image of an Astartes to the wider Imperium. Yet every Legionary bearing the Eye of Lupercal also knows that his forebears failed in defending their Primarch, that their Primarch failed in killing Sanguinius, that the Legion failed to destroy the abominations Fabius Bile created from Horus' cold corpse. Studying each of these failures is an obsession among the ranks of the Sixteenth Legion, one many outsiders have pointed out as unhealthy. The Sons of Horus believe that only by contemplating their past failures can they learn from their mistakes, but others see the damage they are inflicting on themselves by dwelling on their defeats so much.

Interpretations of each failure's reasons vary, and can sometimes lead to brutal intra-Legion conflict, with captains challenging each other in duels – and, in a few extreme cases, open warfare. Some warriors believe that Horus fell because he was weakened by mercy, and so seek to purge themselves of it. Others believe that the Heresy happened because Mankind did not know enough of the galaxy's threats, and spread knowledge of the Warp to those who fight alongside them, going against the Inquisition's will. Such extremism is the principal reason for which the few Sons of Horus who succumb to the call of Chaos fall. Their beliefs and philosophies are slowly twisted by the Ruinous Powers until one day, the warrior wakes up and discovers that he has become what he once abhorred above all else – and that he doesn't care.

But dwelling on the past isn't the defining trait of the Sons of Horus – merely the consequence of what the Sixteenth Legion went through. What lies at the core of their souls is passion, strong and burning as the core of their savage homeworld Chthonia. Channelled through the Legion, that passion takes many form : a battle-rage that can overcome any odds, a sense of brotherhood just as strong as that of the World Eaters, and a dedication to the Imperium that would make a Modominant Inquisitor feel inadequate.

While it has many uses on the battlefield and beyond, this passion must be balanced with discipline and self-control, just as is the case within the Mournival. Chaplains of the Sons of Horus spend as much time tempering their brethren's rage as those of other Legions spend rousing it. Focus is the one virtue exalted above all others : to channel one's burning fury into a cold rage that will make a warrior even more dangerous.

The Sons of Horus also carry on many of the gang traditions of Chthonia with them to the stars, alongside that world's fiery nature. A complex sign language and battle-cant is part of that heritage, as is the tradition of engraving runes of fortitude upon a warrior's teeth. Loyalty to one's brothers and commanding officers is also strong, but those who receive such loyalty must always strive to earn it and remain worthy of it. A deep sense of pragmatism also runs into the Legion, which will consider any course of action in order to claim victory. Despite the infamy the Sixth Legion has brought to the iconography of the wolf, the Sons of Horus have kept a lot of their legacy from the Luna Wolves, which is probably responsible for the fact that the animal hasn't been completely wiped out on every Imperial world. They also use moon emblems to mark their own place in the balance of tempers that makes up the Sixteenth Legion, with the Mournival Lords each adopting a phase of the moon as their own heraldry.

The Horusian Inquisitors and the Exorcist Marines

The tale of how Horus was struck down by an assassin and delivered from possession has endured through the ages. Today, it is an important part of Imperial mythology, telling how the First Warmaster was saved by the noble sons of the Cyclops and his own faithful warriors – a story to teach the importance of loyalty and devotion. But over the millenia, many Inquisitors have regarded the tale in a different light. They believe that this traumatic event gave Horus a clear knowledge of Chaos, as well as an unbreakable determination to see it defeated. Calling themselves the Horusian, they accumulate knowledge of the Ruinous Powers – not their tools or weapons, that only the most extremist of Inquisitors dare to wield – in order to know how to combat it.

The members of this faction seek to emulate the process in order to gain powerful tools against the forces of Ruin. Only by facing Chaos can one gain the knowledge and strength of will required to oppose it, and only by going through the same horrors Lupercal endured can one successfully do so. They subject themselves – or, far more often, their servants – to daemonic possession, quickly followed by exorcism. The rate of survival of these procedures are low, but those who survive with their sanity relatively intact gain a resistance to any psychic powers, complete immunity to further possession, and an undying hatred of Chaos and all its minions. Secondary effects include persistent nightmares for the rest of the subject's life, severe physical trauma, and other mental afflictions.

The more Puritan Inquisitors, of course, consider this practice outright heresy, for it requires the knowledge of daemon summoning and binding, something that could easily be used to create a daemonhost. In their eyes, while noble in intent, it is ultimately just one more step on the path to Radicalism and corruption. And there is some truth to their misgivings : on several occasions, the circles of containment have failed, and the would-be exorcised was consumed by the daemon within, becoming a being of terrible might and evil. Since only the most strong-willed individuals are selected for the procedure in the first place, the daemonhosts created in such catastrophic failures are exceptionally powerful.

Despite this, there are some within the very ranks of the Sons of Horus who are willing to undergo the procedure, seeking to share the same experience as their long-lost Primarch. Space Marines survive the process far more easily than common humans, and receive the same benefits. Among their brothers, they are known as the Exorcist Marines, and are the choice troops of the Sixteenth Legion when facing daemonic foes. However, due to the terrible consequences should the practice become widely known – and quite likely misinterpreted into outright daemonic possession – the Sons of Horus do their best to keep it a secret. The Exorcist Marines do not wear any special insigna, even when they are deployed against the Neverborn – only their brothers and commanding officers know of the great trial they have endured.

Recruitment and Geneseed

The gene-seed of the Sixteenth Legion is untouched by any mutation or defect : all Astartes organs function perfectly, and its rate of viable aspirants is among the higher of the loyal Legions. The only known secondary effect is the phenomenon known as the "True Sons". Making up a sizeable portion of the Sons of Horus, the True Sons are those in whom the gene-seed of Lupercal changes their features into an image of the defunct Primarch. This trait was already present during the Great Crusade, with Horus Aximand being the one who most resembled the Primarch – prior to his disfigurement at Sanguinius' hands. The True Sons are seen as favored by their brothers, and in some Companies, they are selected above their brethren for advancement. The Chaplains and Apothecaries of the Legion, however, are tasked with preventing such favoritism from becoming prevalent in the Legion, to avoid brothers becoming bitter over being ignored for something as insignificant as their looks.

Most of the recruits of the Sixteenth Legion come from Chthonia, but the Sons of Horus keep a presence on many worlds. The Sons of Horus select mostly member of child gangs in the underhives, taking those who display the most strength and cunning, but also the most sense of fraternity. This selection, repeated over the millenia, has caused the gang cultures from which they draw their recruits to evolve, as children embrace the virtues and principles that might cause the Astartes' eyes to fall upon them. While still dark and dangerous places, the underhives of the Sixteenth Legion's recruiting worlds are nowhere near as twisted and corrupted as those of other planets. Besides the hope of drawing the attention of the Astartes, the Sons of Horus have made various deals with the Ordo Hereticus to prevent the growth of cults on their recruitment grounds, as well as with other Imperial organizations dedicated to the help of those in need.

Ironically, while Chthonia itself has remained a hellish environment for ten thousand years, it is frequent for hive-worlds selected by the Sixteenth to become unsuitable for recruitment after a few centuries. As the mentality of the gangs change and the humanitarian organizations spread their efforts, the level of danger in the underhive lowers, and the Sons of Horus end up stopping recruitment altogether. Fortunately, the Imperium is vast, with tens of thousands of hive-worlds with lawless undergrounds : the Sons of Horus are sure to never suffer from a lack of potential recruits.

Warcry

Apart from the Scouts, no warrior of the Sons of Horus would fight in silence. Though they changed their name ten thousand years ago, the spirit of the Luna Wolves is still strong within the Sixteenth, and they howl their warcries as they charge their foes, letting them know exactly who has come to bring them death. The most common cries are 'Lupercal !', 'For the Emperor and the Warmaster !' and the famous call of the Mournival Lords themselves : 'Kill for the living, and kill for the dead !'

Things are different, however, on these occasions when the Sons of Horus face the hated Black Legion. In these battles, there is no battle-cry, no proclamation of vengeance from the Sons of Horus – though the traitors always indulge in taunts and gruesome promises. The mere sight of the Black Legion is enough to cause any warrior of the Sixteenth Legion to fall into a trance-like state of absolute fury. On these battlefields, the sons of Lupercal communicate with each other through signal language and vox-clicks, and those who fight at their side, used to their usual behaviour, are always terrified of this change. The archives of the Inquisition indicate that this practice goes back to the infamous War of the False King, when a plot of the Black Legion resulted in turning warriors of the Sons of Horus against their own brothers.

My father is dead, and I am his son no longer.

Who am I, then ?

I am the beast at the door, half-tamed but still savage.

I am the dog that stays upon his master's grave, waiting for death to take him in turn.

I am the shield and the blade of the Emperor.

I am the spear aimed at the throat of the betrayer.

I am the hunter, hounding the arch-renegade across eternity.

I am a memory, echoing through the ages, waiting for the day of judgement.

I am the wolfhound at the Gates of Hell.

I am death denied.

I am a Legion of One.

I am Cerberus.

---

AN : Lupercal !

Here they are at last. The Sons of Horus, greatest of the Legions, cast down in canon by deceit and consumed by their own unfettered ambition. Here, they are still some of the greatest heroes the galaxy has ever known, but even they aren't spared by the darkness that haunts the forty-first millennium. And yes, I have given the Sons of Horus Exorcist Marines, like those in canon. It just seemed appropriate when I was considering special units for the Legion, considering what happened to Horus here. Also yes, the Interex is gone. No, I am not going to tell you who did it. I am keeping that card in my sleeve for later - maybe in a later Index, maybe for the Times of Ending, maybe never.

This chapter is the one with the longest "Post-Heresy" section, mostly because the Sons of Horus were the ones with the most divergent story at that point from canon. I was also able to add more details about the Black Legion in this universe.

Once again, I have written hints of the Times of Ending, which is really increasing the pressure on me to do it when I am done with the Index Astartes. Next up will be the Word Bearers, who are perhaps the one loyalist Legion the most different from its canon counterpart. Yes, even more so than the Night Lords and the World Eaters. You will have to take my word for it until I am done with them ... which won't be anytime soon, I fear. I am going to write the next chapter of Warband of the Forsaken Sons next, and between that, the scenarios for my games of Black Crusade (more on that later) and the ten Chaos Flavor Quotes I write each day (which you can find on the Spacebattles forum), I don't have much free time left.

I would like to thank Jaenera Targaryen for beta reading this chapter. Check out the story Blood of Ignorance, taking part in the Roboutian Heresy verse and featuring the Thousand Sons ! And don't forget to take a look at Nemris page on deviantart. His artwork for the Roboutian Heresy is simply amazing - and the latest piece, on Cato Sicarius, is simply hilarious if you read the title in the appropriate voice (for those of you who don't get that last bit, watch the web series If the Emperor had a Text-to-Speech Device, you will understand).

I have another announcement to make : last time I published something, I asked for volunteers to test a simplified RPG system. I am happy to announce that there were replies, and right now, I have three weekly games of Black Crusade running (for some reason, being an Heretic interests my readers more than being an Acolyte of the Inquisition). If you are interest in joining one of these games, don't hesitate to contact me, and we will discuss how to integrate a new character to one of the stories.

Well ... I don't think I have anything more to say today. Please follow and favorite, but more importantly, review and tell what you think of this chapter and what you want to see in the next ones !

Zahariel out.