The Battle for Grand Al'gul was a series of running battles fought by the Fire Angels Space Marine Chapter against the Chaos Space Marine warband known as The Sanctified on the Cemetery Worlds of Grand Al'gul System in 666.M41, at the behest of the Inquisition. The Fire Angels acquiesced to the Inquisition's request and diverted from their course to intercept this powerful Chaos warband.
During this campaign against the Chaos Space Marines and their daemonic minions, the Fire Angels blocked their efforts to desecrate the resting places of the honoured Imperial dead and work hideous Chaos rituals in the ruins. These were fraught and brutal combats where not only the lives but the souls of the Space Marines were at stake.
The Fire Angels Astartes succeeded in forcing their enemies to fight them in a series of assaults and counter-assaults, with the Fire Angels maintaining disciplined order and using the cover provided by the marble forests of headstones and maze of burial vaults to their advantage. The Sanctified responded with all the foul sorceries at their command, liquefying stone with their dark magicks and summoning roiling, chattering swarms of mindless daemonic beasts to harrow those that would dare to oppose them.
The Fire Angels paid a heavy price in the short but savage combat before victory was achieved, including the martyrdom of their Chapter Master Haran Stark in battle against a frost-rimed Greater Daemon of Tzeentch, known as a Lord of Change, while defending the sacred Narthex of Penitents, and the self-immolation of their Chief Librarian Mathias Dee in order to avoid Warp-possession.
Eventually, their forces spent, The Sanctified were driven from the sacred sites and routed from the system; the planned apotheosis of The Sanctified's Arch-Sorcerer Ezrath Cull to daemonhood thwarted. Following the defeat of the corrupted Heretic Astartes, Cull, a once-favoured Champion of Chaos, was assassinated by his own apprentices in a brutal power struggle to control the shattered remains of his decimated warband as they fled Grand Al'gul.
- Imperial Armour Volume Nine - The Badab War - Part One, pp. 92-93