Event · M31
Horus Heresy
The Horus Heresy (005–014.M31) was a galaxy-spanning civil war led by Warmaster Horus Lupercal against the Emperor of Mankind. Horus, Primarch of the Sons of Horus Legion and the Emperor’s appointed military commander, turned against his father at the height of the Great Crusade and sought to seize the Imperium of Man, governed from Terra. The war divided the Space Marine Legions, the Imperial Army, and the Mechanicum, and ended only with the Siege of Terra, fought at the Imperial capital itself. Several grievances prepared the ground for rebellion. The Emperor’s withdrawal to Terra to pursue an undisclosed project, shared with none of his sons, bred resentment among the Primarchs, as did the Council of Terra, a body many saw as usurping their authority. Lorgar Aurelian of the Word Bearers, publicly rebuked by the Emperor for encouraging worship of him as a god, turned his Legion toward the Ruinous Powers and seeded Warrior Lodges throughout the other Legions that later carried Horus’s conspiracy. Horus himself turned after being gravely wounded on Davin by a Chaos-tainted blade; during his recovery he was shown visions, engineered by the Word Bearers chaplain Erebus, that played on his pride and his resentment of Terra’s bureaucracy. A warning from Magnus the Red, Primarch of the Thousand Sons, went unheeded, and Horus accepted the Chaos Gods’ pact, renouncing his oath to the Emperor. Horus won roughly half of the Legions to his cause, including the Emperor’s Children under Fulgrim and the Iron Warriors under Perturabo, with elements of the Imperial Army, the Mechanicum, and several Titan Legions. He masked his intent by purging dissenters within his own force at Isstvan III, then luring loyalist Legions, among them the Salamanders, Raven Guard, and Iron Hands, into the massacre at Isstvan V. The war spread rapidly: the Word Bearers struck the Ultramarines at Calth, Leman Russ led the Space Wolves against Magnus the Red’s Thousand Sons at Prospero, and Sanguinius and the Blood Angels fought a costly action at Signus Prime before the vast war zone of Beta-Garmon consumed forces on both sides. The Heresy climaxed when Horus brought the traitor fleet to Terra itself, defended by Rogal Dorn’s Imperial Fists, the Legio Custodes, and the assembled loyalist forces in the Siege of Terra. Sanguinius fell in combat against Horus before the Emperor confronted the Warmaster in person aboard his flagship, the Vengeful Spirit, and slew him, though the effort left the Emperor mortally wounded and dependent on interment within the Golden Throne. The defeated traitor Legions withdrew into the Eye of Terror, and the Imperium turned to the Great Scouring to hunt down the remnants of the rebellion. The Horus Heresy ended the Great Crusade’s expansion and left the Imperium under the regency of Roboute Guilliman, who began reorganising the shattered Legions in its aftermath. As the fracture from which the present age of the Imperium was born, it remains the pivotal event against which all later Imperial history is measured.
See where Horus Heresy occurred on the galactic map during the Horus Heresy.