The Witch king of Angmar remained indifferent to the grand host assembled before him. Countless Legions of Orcs marched by him and his beast in pathetic attempts at organized columns. The towering armored forms of the Olg-hai which march with them being the only formidable aspect of this force. But the host of Mordor wasn't what had his interest, no, that would be the host of their new ally.
The demons of Hell had no semblance or organization, but the power each of them emanated was beyond anything the Witch King had witnessed before aside from Sauron himself. From the Hell Barons which matched the height of Olg-hai, their metal limbs glistening in the high noon sun. To the Revenants which soared over the land on torrents of fire, and the Imps, the most numerous of the demons, but each individual having the capability to tear Orcs apart with ease.
Tens of thousands now march to bring ruin to the world of men, and as the Witch King took to the sky, the ruined city of Osgiliath would be the first to fall.
...
It was chaos, cries of alarm had echoed from the eastern wall indicating the approach of the enemy. But that is not what caused this scene of near panic, for the threat of Mordor was nothing new, what caused it was the horde coming towards them now. Beasts the likes of which they had never seen before, with a terrifying speed and ferocity. But Faramir knew he nor anyone else could afford to panic. So with as much courage and discipline as he could muster, he bade the garrison to ready themselves. "A great enemy is upon us! To battle sons of Gondor!"
Fortunately his words seemed to have an affect. Units of archers began to swarm atop the wall as other soldiers rushed to their positions. The ten trebuchets which supplemented the defense loosed an opening salvo of boulders which sailed through the air towards the tide of beasts. To their surprise, a few of the boulders were shattered while in the air, courtesy of weapons fire from a swarm of Revenants and some Mancubuses on the ground, but the rest made impact, each tearing bloody swaths into the mass. But the hordes momentum did not slow. Minutes passed as the distance closed, until the defenders could begin loosing arrows, preceded by another volley of boulders. Each Gondorian arrow flew true, slaying fodder by the hundreds, with some of their stronger brethren joining the dead, a few lucky shots even slew Mancubuses.
But they just kept coming, the demons pressed on towards the wall, uncaring of their dead. Faramir shot down a Revenant that got to close, the arrow piercing it's skull, but his thoughts were drawn to the peculiar nature of this attack. For if they had the means to destroy boulders, surely they could breach the walls without trying to scale them, and without ladders or siege equipment on top of that.
As it would turn out, no such equipment was necessary. For as the fodder reached the wall, they sunk their claws deep into the stone and scaled upwards with frightening speed, managing to catch a few soldiers off guard, either tearing into them or throwing them off the wall. Those that were able to draw their swords in time quickly moved to engage them. The quick response barely enough to stem the tide. But their efforts came at a cost, for dozens were killed in the first few moments and hundreds more would die as steel met claw in this violent dance. The limitless numbers of the enemy serving to exacerbate their current situation.
Faramir and his rangers did what they could to support their allies, some sending lethal volleys of arrows into the enemy, with others including Faramir drawing thier swords and joining the melee. But despite the effort, the defense was starting to crumble under the weight of the assault, and the rockets of the Revenants killing swaths of Gondorian soldiers, without care for their allies caught in the blasts. The situation was being intensified by a bombardment directed at the walls of Osgiliath. With growing panic at having noticed this, Faramir shouted out an order to fall back, but it was too late, for sections of the wall began collapsing under the bombardment, taking the soldiers and demons on top with it.