Horus Heresy

The Horus Heresy marked the end of the Great Crusade.

During the heresy, the forces of Chaos showed themselves to several Space Marine legions. This action corrupted these Legions for Chaos's tasks. Foremost among these corrupted Chaos Space Marines was Warmaster Horus, who until then had been considered the greatest warrior of humanity.

These renamed "Chaos Space Marines", abandoning their earlier charge, began a trek back to Terra (Earth), laying waste to their former allies holdings along the way.

Eventually, these corrupted marines landed on Terra, experiencing heavy resistance from several loyal Space Marine legions. Victory seemed to be assured, until Horus let his guard down to watch the final breakthrough and destruction of the Imperial Palace. The Emperor saw this opportunity and teleported to the Warmaster's personal battle barge with two of his Primarchs. In an epic scene that would burn itself into the minds of all battle-brothers of the Blood Angels chapter, the Primarch Sanguinius fought Horus in single combat, wounding the fallen warrior. But Horus power was too great and Sanguinius fell. At this point the Emperor charged in and assaulted the Warmaster Horus. The Emperor was successful in defeating Horus, but only barely; he lay dying as well. Due in part to his psychic skills, the Emperor survived long enough to be transferred to a "Golden Throne" - a strange mechanism that would allow him to survive forever in a state of undeath.

After the failure of the Heresy, the remaining Chaos Space Marines retreated into the Eye of Terror, from which they periodically launch Black Crusades into the Imperium led by Abaddon the Despoiler, clone-son of Horus.

Horus Heresy is also the title of a collectable card game produced by Sabertooth Games, and an out of print Games Workshop game, both based on these events.