Saint Basillius was an Imperial Saint. An enormously influential figure who rose out of the Ecclesiarchy purges of the Age of Redemption, Basillius commanded a "Puritas" division of Space Marines who eliminated those he deemed heretical or impure. In 321.M37, he declared thirty Space Marine Chapters' faith to be lacking, condemning them to the Abyssal Crusade in the Eye of Terror.
In early M38, Chapter Master Konvak Lann of the Vorpal Swords led the survivors of the Crusade out of the Eye of Terror, having purged at least four hundred worlds. However the Chapter Master declared the now-ancient Saint Basillius to be a false idol who had in fact been an apostle of Chaos working against the Imperium. Worship of him was banned, his followers were massacred, and his remains and relics were loaded onto a freighter and launched into a nearby star.
- 1: Warhammer 40,000 6th Edition Rulebook, pgs. 170-171
- 2: Codex: Chaos Space Marines (6th Edition) pg.18-19