The 13th Black Crusade was the greatest of the assaults launched from the Eye of Terror by Abaddon the Despoiler, heir to Horus and champion of the Chaos Legions. Where his twelve previous incursions had merely tested the Imperium's defences, this thirteenth was intended to break them utterly, and in its opening years it succeeded beyond even his ambitions.
Abaddon hurled a vast host against the fortress world of Cadia, the bastion that had turned back Chaos for ten thousand years and guarded the only stable passage from the Eye. Alongside daemon engines, traitor warbands, and corrupted war machines came a cunning strategy aimed not merely at conquest but at the very fabric of reality. The defenders held with legendary stubbornness, yet the sheer scale of the onslaught ground them down.
The crusade's climax was the fall of Cadia itself, an event without precedent in Imperial history. Its destruction helped tear open the Great Rift, a wound in the heavens that split the galaxy in two and plunged half the Imperium into darkness. Though Imperial forces evacuated what survivors they could, the strategic catastrophe was total: the gate had been thrown wide, and the long defence of the Cadian Gate was ended forever. Abaddon had at last delivered the blow his master never could.