Iron Warriors

The Iron Warriors, who were originally the IVth Legion of Space Marines, specialised in the breaking of sieges and assaults on static fortifications, which made them great rivals of the Imperial Fists Legion, said to construct the greatest static defences in the Imperium. It was this rivalry between the Legions, and between their primarchs Perturabo and the Imperial Fists' Rogal Dorn, that helped turn the Iron Warriors to Chaos.