Event · M30–M31
Great Crusade
The Great Crusade (late M30–M31) was the Imperium’s galaxy-wide reunification campaign, led from Terra by the Emperor and the primarch-led Space Marine Legions. It followed the Unification Wars that had first brought Terra itself under a single rule, and it began once the Emperor judged the home world secure enough to look outward. From Terra the Emperor dispatched Expeditionary Fleets, each built around a Space Marine Legion and its attendant Imperial Army regiments, Mechanicum forces from Mars, and civil administrators, with the stated purpose of finding the scattered primarchs, ending the age of isolation that had followed humanity’s earlier age of strife, and bringing independent human worlds into Imperial compliance by treaty or by war. Over roughly two centuries the Crusade’s fronts expanded outward from the Sol system under the nominal coordination of Malcador the Sigillite and, later, the war councils convened around individual primarchs as each was recovered and given command of his gene-legion. Contemporaries of the Crusade at its height included all eighteen primarchs and their Legions, the Mechanicum priesthood of Mars, and the many human successor states and xenos polities the fleets encountered, from compliant remnant colonies to the Interex and the greenskin empires cleared during campaigns such as the one that culminated at Ullanor. The Crusade’s furthest and most celebrated expansion is associated with Horus, who was raised to Warmaster at Terra’s command following the Ullanor Triumph, taking overall field authority for the continuing campaigns while the Emperor withdrew to Terra to pursue other work. The Crusade’s momentum broke when Horus turned against the Emperor, beginning the Horus Heresy in the early thirty-first millennium and drawing several Legions and expeditionary forces into open civil war rather than continued expansion. Many fronts opened during the Crusade were left unfinished or were abandoned as Legions were recalled or turned to one side or the other, and the era of galaxy-wide conquest gave way to the Imperium’s long defence of what had already been claimed. The Great Crusade is remembered as the formative campaign of the Imperium’s borders and institutions, and its unfinished business, broken alliances, and interrupted compliances remain reference points for later Imperial history centred on Terra.
See where Great Crusade occurred on the galactic map during the Horus Heresy.