The 13th Black Crusade

The 13th Black Crusade was the culmination of ten thousand years of Chaos ambition, the assault in which Abaddon the Despoiler at last shattered the bastion that had held his masters' fury in check. Where twelve prior crusades launched from the Eye of Terror had been bloodily repulsed, the thirteenth would break not merely a world but the galaxy itself.

Abaddon flung the massed traitor Legions, daemon hosts and cultist armies of the forces of Chaos against the Cadian Gate, the fortified corridor that was humanity's only reliable path past the great warp storm. The Astra Militarum, Space Marines, Adeptus Mechanicus and even Aeldari allies threw everything they possessed into the defence, and the void and the surface alike were drowned in fire and slaughter on an almost unimaginable scale. Warp storms raged across the sector as the great crusade advanced, and countless worlds beyond number were consumed in fire and madness in the Despoiler's wake. For all the valour of the defenders, the sheer weight of the assault could not be denied.

Despite the heroism of the defenders, the Despoiler had learned the hard lessons of his previous defeats. His true objective was never simple conquest but deliberate destruction: to topple the ancient necron pylons whose hidden power had long suppressed the warp across the entire region. When Cadia's surface was cracked open and a captured Blackstone Fortress driven down upon it, the world was doomed and its stabilising influence upon reality undone forever.

With the fall of Cadia the Great Rift tore open across the heavens, severing half the Imperium in howling darkness and cutting it off from the light of the Astronomican. It was the worst catastrophe to befall mankind since the Heresy itself, and it is chronicled at length in the account of Abaddon and the Black Crusades.