Event · M41–M42

Opening of the Great Rift

The Opening of the Great Rift was the emergence, around 999.M41, of the Cicatrix Maledictum, a warp rift that divided the Imperium of Man. It followed Abaddon the Despoiler’s 13th Black Crusade and marks the close of the Indomitus-preceding age of the Imperium and the start of the era the Imperial Calendar now reckons from the rift’s appearance. The rift is the pivotal event of the galactic setting in the late forty-first and early forty-second millennia, and the origin of the present division between the Imperium Sanctus and the Imperium Nihilus. The Great Rift extends across the galaxy from the Eye of Terror in the galactic west to the Hadex Anomaly on the Eastern Fringe, passing through the region of the Segmentum Solar on its way. Holy Terra and the greater part of the Imperium’s former territory lie on one side of it and are known as the Imperium Sanctus. Worlds cut off beyond the rift’s reach, together with the region in which the light of the Astronomican is obscured, are known as the Imperium Nihilus. No single cause for the opening is firmly established. The fall of Cadia and the destruction of its blackstone pylons during the 13th Black Crusade removed a barrier that had long contained the Eye of Terror, and this is the explanation most often given. Other accounts attribute it to sorcery worked by the Daemon Primarch Magnus the Red during the Thousand Sons’ assault on the Fenris system, or to disturbances in the webway and among the Aeldari, including the stirrings associated with Ynnead. These explanations are not mutually exclusive, and the rift’s emergence followed years of worsening warp turbulence that had already disrupted Imperial travel and communication. The opening released a surge of warp energy and psychic darkness across the galaxy, recorded in the Imperium as the Noctis Aeterna. The Astronomican was obscured, navigation and astropathic communication failed across large regions, and fleets, armies and whole worlds were lost or isolated. Warp storms of unprecedented severity followed: some circle the rift permanently, while others range across the galaxy, cutting sectors off from Terra and exposing them to invasion by the forces of Chaos. The accompanying distortions of time and space were serious enough that Roboute Guilliman, the Primarch of the Ultramarines returned to active command, ordered a reform of the Imperial Calendar, dating the new era from the rift’s opening. Guilliman’s principal response was the Indomitus Crusade, in which he led a war host of Adeptus Custodes, the Adepta Sororitas and Silent Sisterhood, and newly raised Primaris Space Marines to relieve besieged Imperial worlds on both sides of the rift. Among the worlds it reached was Baal, the home world of the Blood Angels, whose defenders were then contending with Hive Fleet Leviathan. Elsewhere in the Imperium Nihilus, isolated worlds faced daemonic incursion, xenos attack and the collapse of central authority without the prospect of relief. The rift has continued to spread and roil in the years since, and it is credited with a marked rise in psychic phenomena across the galaxy, a trend some name the Psychic Awakening. The Opening of the Great Rift is accordingly reckoned the hinge between the 13th Black Crusade that preceded it and the long era of daemonic incursion, siege and crusade that followed, including the campaigns fought during the Noctis Aeterna and the continuing course of the Indomitus Crusade. On the Orrery map its anchor is the Eye of Terror, the western terminus of the rift; on the timeline it is bound to the fall of Cadia and to the Cicatrix Maledictum, which remains the defining feature of the galaxy in the present era.

See where Opening of the Great Rift occurred on the galactic map in the 41st Millennium.

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