Event · M31
Ruinstorm
The Ruinstorm was a warp storm that severed much of the galaxy from safe passage during the Horus Heresy, active from 007.M31. It was deliberately raised by Lorgar, primarch (one of the Emperor’s gene-forged sons, each the commander of a Space Marine Legion) of the Word Bearers Traitor Legion, to isolate the Emperor’s loyalist forces from Terra and from one another, denying the Imperium of Man any coordinated response to the rebellion of the Warmaster Horus. The storm’s genesis lay in the Calth Atrocity, in which the Word Bearers turned upon their unsuspecting allies of the Ultramarines Legion at Calth, within the Five Hundred Worlds of Ultramar. Amid the slaughter, the Word Bearers’ First Chaplain Erebus unleashed the Ruinstorm as an offering to the Ruinous Powers, drawing on the death and despair of the massacre. Lorgar subsequently fed and expanded the storm through the atrocities of his Shadow Crusade, so that it grew in size and violence for years afterward. While the Ruinstorm raged, the immaterium (the warp, through which starships travel and telepathic messages pass) became largely unnavigable to loyalist fleets and psykers, though Lorgar and his followers retained secret paths through it. Daemonic hosts spilled into realspace in its wake, afflicting worlds cut off from Imperial aid. Fearing Terra lost, Roboute Guilliman, primarch of the Ultramarines, established the short-lived successor state of Imperium Secundus as a contingency, and it was only through the alien Pharos device that his fleet found safe passage to regroup at Macragge.
See where Ruinstorm occurred on the galactic map during the Horus Heresy.