Warhammer: Horus Heresy - Legions Imperialis

Horus Lupercal, Warmaster of the Emperor's armies, has turned upon his gene-father and sent the Imperium spiralling into bloody civil war. Half of the great Space Marine Legions have sided with the traitorous Warmaster, and countless cohorts of the Solar Auxilia, Knight Households, and Titan Legions march at his side. Now brother fights brother as the Imperium's vast armies tear one another apart in a cataclysm of fire and blood. An age of darkness descends, the likes of which have never been witnessed before.