The Iron Warriors once formed the Emperor's most able body of siege troops. The Iron Warriors' Primarch, Purturabo, excelled in siege and warfare above all else. Wherever the Iron Warriors fight they throw up great evil citadels in their wake, and hold them against all comers. Fields of trenches and forests of razorwire surround the strongholds of the Iron Warriors. Even after Horus's defeat, the Iron Warriors were only driven out of the Imperium worlds at a terrible price.
Codex Chaos 2nd ed.
The Iron Warriors once formed the Emperor's most able body of siege troops. They fought alongside the Imperial Fists on a hundred worlds in the Great Crusade, laying siege to alien citadels and the palaces of heretics who denied the Emperor's divinity. The Iron Warriors' Primarch, Perturabo, excelled in siege and trench warfare above all else, and his treatise on fortifications and their destruction formed the basis of several sections of the Tactica Imperium. The Iron Warriors betrayed their oaths to the Emperor in the wake of the drop site massacres on Istvaan V. In accordance with Perturabo's doctrines the Iron Warriors, had rapidly established strongholds and trench systems around their drop zones. The loyalists Space Marine Legions which had suffered tremendous casualties during their initial deployment found themselves driven back against the Iron Warriors' fortifications by the ravening Traitor Legions. Instead of offering the hard-pressed loyalists respite the bunkers and bastions proved to be their graveyard as the Iron Warriors mercilessly gunned down anything which moved within range. With the bloody rattle of heavy bolters and the slicing beams of lascannon the Iron Warriors declared for Horus. After Istvaan the Iron Warriors split up to fight on a dozen other worlds in the Heresy. Contingents of Iron Warriors led assaults by the Chaos hordes against the Imperial palace on ancient Terra. They fought on Vanaheim, reducing its armored cities to twisted ruins one after another. They battled across Thranx and Avellorn, worlds where every scrap of ground is covered by plasteel and rockrete. They struck at loyalist fortresses, temples, keeps and palaces across the galaxy and ground them beneath the tracks of their siege tanks. Wherever the Iron Warriors fought they threw up great evil citadels in their wake and held them against all comers. Jagged towers mounting heinous weapons of destruction dominated the surrounding terrain from these monuments to Perturabo's cunning. Fields of trenches and forest of razor wire surrounded the Iron Warrior's strongholds such that the loyalist began to dread the bloody assaults needed to destroy them. Even after Horus's defeat the Iron Warriors were only dislodged from the Imperium's worlds at a terrible price. The surviving Iron Warriors were driven back into the Eye of Terror. There they took a world for their own and fortified it against all comers. Freed from the shackles of physical laws the Iron Warriors' battlements and turrets rose spiraling upwards for miles. Their oubliettes and dungeons pierced the world to its core, donjons and bastions sprang forth like fungi until no world has left, only an impossible tangle of insane structure, a madman's architecture of iron and stone where twisted stairs run at right angles to one another and pinnacles plunge eternally downwards. Within this impossible fortress countless warbands of the Iron Warriors lurk and plot how to crush and imprison all beneath their rule.
