The Fourth Legion -

"Iron Without!" roared his Legionaries as they advanced, not running, but walking in a relentless, iron wall. The Imperial Fists fired from the breaches, but the IVth Legion simply ignored the casualties. They were used to taking suicide missions, forced by their primarch, Perturabo, to excel in hopeless situations.

The Fourth Legion didn't celebrate. They simply packed their artillery and began moving towards the next fortress, another, more difficult challenge, for they were the masters of iron and the servants of a war that would never end. The Fourth Legion

On the fourth day, the firing ceased. The silence was heavier than the noise. Then, Valerius gave the order. "Iron Within." "Iron Without

"They have had eighteen months to fortify this position," whispered his second-in-command, Berossus, over the vox-channel. The Fourth Legion didn't celebrate

The Iron Warriors (IVth Legion) are known for being master siege-breakers, pragmatic yet bitter warriors who specialized in breaking down static defenses, often in competition with the Imperial Fists.*

"Record this," Valerius told his sergeant. "Bastion 4-Alpha fell in four days. The Fists are efficient, but the Iron Warriors are inevitable."