Welcome to my first real crossover story, What Was Once Forgotten. A Warhammer 40k/ Harry Potter crossover. I just started writing this today and I'm not sure what direction it will be moving towards. Leave a review and let me know what you think and any suggestions you might have.

I don't own Harry Potter nor do I own Warhammer 40k.

Missiles and rockets screamed through the glowing atmosphere, racing towards their targets. In the distance the explosions could be heard and felt shaking the ground. The shells and missiles had been incessant ever since the soldiers had made landfall.

Landfall had been rough, very rough. Of the three dozen troop carriers that were attempting to land on the planet over half of them had been destroyed by the anti-aircraft emplacements that were supposed to have been destroyed by the orbital bombardment. This had evidently not happened, and more anti-aircraft guns had sprung out of concealed and heavily protected bunkers and had wreaked havoc on the invading soldiers.

These invading soldiers were the 19th Cadian Regiment of the Imperial Guard. The planet they had landed on was simply known as HW567398, a Hive World that had fallen away from the Imperial path and had forsaken the Emperor. Various cults had popped up inside the large hive city, and the PDF and Arbiters had proven themselves riddled with corruption and traitors.

When the cults were first noticed and attempted to be subdued all hell had broken loose.

Upon being ordered to put down the small riots and revolts dozens of the Arbiters had refused and had revealed themselves as traitors and had joined the rioting and some of the cults. The same had happened when the PDF forces had been called in by the Imperial Governor.

That had been six months ago. The Governor had immediately called for support, and the 19th Cadians had been the closest Imperial Guard regiment and had responded as such. They had received orders from the commanding general of the force that they had split off of that they needed to bring the hive world back into the fold at any cost, to either the world or it's citizens.

It was in fact an infestation of cultists and heretics, and would have to be dealt with as such.

What no one had expected in the six months that the 19th had been in transport, was that the cultists and rioters had organized themselves into a formidable fighting force. This was not only surprising but was also quite worrying for the command of the 19th Cadian. It had been nearly completely unexpected that they would face an organized and competent enemy, and while it had seemed that the orbital bombardment had been effective it was now clear that it was not.

That was the first surprise in a campaign that was sure to be filled with dangerous, nasty, surprises that were sure to take more lives from the already devastated forces of the 19th Cadian.

Corporal Ibsen was currently taking shelter in a bombed out hab building that was inside the very first hab district that had been shelled from orbit. After the disastrous landing of the first wave the Cadian forces had scattered, each platoon breaking off from their battle groups and just trying to survive. It had become difficult to raise any of the other platoons on the vox, which was making Corporal Ibsen's life much more difficult than it could have been.

He had about ¾ of the troops that he had been deployed with, which was much better than some of the other platoons.

The raving mass of cultists and heretics that Ibsen had been tasked with killing could be seen slowly making its way through the hab block heading towards where Ibsen's platoon had taken shelter. While the enemy was poorly equipped and even more poorly trained they still outnumbered the Guardsmen at least 5 to 1, even after a full day of an intense running battle filled with skirmishes and ambushes on both sides.

"Incoming!" A mortar shell could be heard whistling to their position of relative safety, and all of the nearest troopers dove for cover. Corporal Ibsen stood firm and tall, he knew that he should be taking cover with his men, but he also knew that a pivotal moment was coming in the battle for survival that he was currently facing.

His troops saw him facing the incoming danger with a stony and resolute face and were inspired. Their hearts were lifted by their leader's courage in the face of immediate danger, and the shell fell short of the hab building and blew a small crater into the roadway outside. A small cheer rose among the men and Corporal Ibsen raised his voice, "The enemy are drawing near. We shall hold them here as long as possible. Prepare yourselves and stand tall. Emperor be with us."

Moving back into a slightly better position to command his troops more effectively Corporal Ibsen saw them taking up favorable firing positions and positions of cover.

They had few heavy weapons left, but had set up their single heavy bolter at the best possible area that would allow a clean line of sight and optimal firing zone. This would not be so much a strategy intense battle as it would be a battle of attrition that the Guard was sure to lose. While a victory here was possible, especially because of the poorly equipped enemy, the enemy would be able to send more and more reinforcements until Ibsen and his men were completely overwhelmed.

Reviewing his current options one more time Corporal Ibsen sighed. He could turn east and attempt to run from the advancing mob, which was now only a few short minutes away, but his troops would be overrun and slaughtered in the open roadway when the mob caught up with them. The mob was approaching from the north, making a northward escape impossible, and the west was effectively blocked by a massive hive spire that had fallen and crushed dozens of habs. While his men could traverse this obstacle it would take more time than they had available. And to the south they could not escape very far. Within a few hundred meters a large wall that separated the districts from each other would cut off their retreat entirely. The best option currently was to stay where they were and fortify as best as possible. Ibsen turned his attention back to the present as a whooping cheer could be heard as the large mob rounded the corner and the heavy bolter began to bark out a fast and steady rapport.

The thick mass of bodies kept pressing forward, despite taking heavy losses as the Guardsmen opened fire with their lasguns. The steady advance, which had quickly turned into a running charge was taking heavy casualties, leaving dozens of broken and bloodied bodies in the street.

Hiss-Crack…Hiss-Crack

The sound of the laspistol that Corporal Ibsen was firing from his position soon was soon indistinguishable from the sound of dozens of other lasweapons. The occasional 'chunk' sound of a grenade launcher could be heard coming from somewhere to his right, and Ibsen nodded slightly at the effective use of grenades against such a tightly packed enemy.

Between the heavy bolter and the grenade launcher the charging mob had been reduced, but they were still approaching at a rapid pace.

Ibsen's voice could suddenly be heard ringing loud and clear across the battlefield. "Fix bayonets! Hold firm and we'll be out of this yet!" As the guardsmen fixed their bayonets many were becoming more nervous than they had been in the beginning of the engagement. The entire day had gone from bad to worse ever since their botched landing.

The charging mob reached the Guardsmen just as most of them finished attaching their bayonets, and the two groups clashed in close combat. Clubs, bottles, rocks, and the occasional sword or blade clashed against bayonet, chainsword, and lasgun. The cultists now had left the dangerous kill-zone that had been created and had entered close combat with the Guard, which was where their numbers would be a large advantage.

The heavy bolter and grenade launcher fell silent, the bolter emplacement beign over-run by the mob and the soldier wielding the grenade launcher had fallen to a cultist with a rusted vibro-blade. More and more casualties were being taken by the Guard forces, and Corporal Ibsen and what was left of his once five man command squad prepared themselves to enter the melee.

Retrieving his chainsword and revving the blade Ibsen and his three troops waded into the combat.

Rending one cultist with his blade while loosing a point-blank lasshot into the skull of another cultist Corporal Ibsen could see that the battle was slowly falling more to the side of the charging cultists. Rage flared up in his heart as he saw a group of his soldiers be completely overrun and killed. The battle was nearly lost, if it could be called that, it was more of a bloodbath that had at first been in favor of the Guard and then in favor of the mob.

As he continued to slash and stab with his chainsword Corporal Ibsen could not discern or identify any sort of commander or any command structure at all among the mob of heretics. This was not terribly surprising, the group had likely been simply roving around and looting prior to discovering his platoon and attacking. They had been attacking the platoon for the better part of the entire day, and in result had their numbers cut in half.

But this was not the most important thing right now for Corporal Ibsen. His troops had been effectively overrun, with a few of the squads on the edge of the conflict routing and breaking off from the close quarters fighting. Ibsen saw this and felt the urge to spit in disgust, he had not given any order to retreat or fall back, and he would not give the order.

He had sometimes been described as too harsh or too 'by the books' by his troops. He was sometimes too slow to react to a changing situation on a battlefield and his troops suffered for it.

But neither his flaws nor the routing of some of his forces were the most important thing currently.

A faint roaring could be heard coming from far overhead, and at first neither side paid much attention to it. No one knew the true importance of this noise, but they soon would.

The roaring became more and more pronounced, not that it much mattered to the fifteen or so troopers left standing with Corporal Ibsen at their center. The fighting had lulled for a moment and they had regrouped for a last ditch defense. Looking into the sky as the roaring noise suddenly became identifiable Corporal Ibsen shouted to his men, "Incoming drop pod!"

One of the troopers yelled "It's the Space Marines! We're saved!" A cheer rose from the remaining Guardsmen and it seemed that the battle had immediately changed in their favor. The mob that had been preparing for a last assault to kill the Guardsmen suddenly broke and bolted.

The squads of retreating Guardsmen that had routed earlier had reformed and returned to Corporal Ibsen's remaining group. They would be punished severely, if any of them at all managed to survive the day, which was now seeming more and more likely as the drop pod slammed into the roadway of the hab block, crushing a few of the cultists underneath it's massive weight.

Steam hissed from the pressurized drop pod as the doors dropped down, crushing a few more of the quickly retreating mob. As the door fell open a twin-mounted automatic bolter opened fire into the backs of the cultists, and three massive Astartes sprang outwards from the drop pod, pursuing the fleeing mob of heretics.

Being the first to recover from gaping slightly at the magnificent sight of the Astartes Corporal Ibsen rallied his remaining troops to himself. Gathering all of his soldiers to him Ibsen looked to see the three Astartes tearing their way through the heretic mob.

They were all massively tall, with their black painted armor with white trim and bright red eye slits in the helmets. The decorations and livery on all three of the Astartes were impressive, they were all veterans of dozens of campaigns, but what stood out was the Captain's rank on the Astartes that was currently twirling a deadly dance with his glowing power sword in one hand and bolt pistol barking off shots in the other. The two other Astartes were also killing very efficiently. One had a massive heavy bolter in his hands, and as he swept the barrel back and forth dozens of heretics met their painful end. The other had a chainsword and bolt pistol and was using both to deadly effect.

The bolter mounted inside the drop pod had fallen silent, but this was hardly noticed by Corporal Ibsen and his men. They were watching in awe as the three Space Marines did what they do best, and while no one wondered out loud they were all wondering where they had came from, what chapter they belonged to, and why they were here. It was quite the puzzle, but Ibsen decided to not worry about it too much. They had been there to intervene and save the Imperial Guardsmen, which had saved their lives.

Within a few minutes the Astartes had mowed down or otherwise slaughtered all of the remaining mob, a group of around fifty or so. Moving back towards their drop pod the three Astartes were greeted by three squads of bowing Guardsmen and Corporal Isben with his head bowed.

"Thank you for saving us, lords. You arrived just in time."

The Captain stepped forward and removed his helmet, revealing short black hair and piercing green eyes, and spoke. "I am Captain Hadrian Potter, of the Forgotten Warriors."

Well that was the first chapter. Let me know what y'all think and leave a review. I just started writing this on a whim today, but you should expect to see more of it.