M31


 * ca. 150.M31 - The world of Karis Cephalon is resettled by the Imperium of Man during the Great Crusade.
 * ca. 205.M31 The Horus Heresy Begins; The Battle of Isstvan III - The Warmaster Horus gathers together the first 4 Traitor Legions of Astartes, including the Sons of Horus, the Death Guard, the World Eaters and the Emperor's Children, and virus-bombs Istvaan III while Loyalist elements of the four Legions are operating on the surface to suppress a minor rebellion against the Imperium in Istvaan III's capital of Choral City. Horus hoped to destroy any remaining Loyalist elements within the Legions under his initial command in a single fell betrayal. However, the virus-bombing fails to destroy all the Loyalist elements on the surface and Horus' plans are delayed for a crucial period of time by the resistance offered by the remaining Loyalist Space Marines under the leadership of Captain Saul Tarvitz of the Emperor's Children and Captain Garviel Loken of the Luna Wolves. A Loyalist Death Guard Frigate with the Traitor fleet in orbit of Istvaan III called the Eisenstein successfully escapes through the Warp to Terra after being rescued by the Imperial Fists Legion's massive mobile fortress-monastery Phalanx and brings the news of Horus' corruption by Chaos and his betrayal of the Imperium to the Emperor of Mankind.
 * ca. 205.M31 Drop-Site Massacre of Istvaan V - Seven Space Marine Legions -- the Iron Hands, Salamanders, Raven Guard, Alpha Legion, Night Lords, Iron Warriors, and a large contingent of Word Bearers are sent by the Emperor against the 4 Traitor Legions of Horus at the world of Istvaan V, but 4 -- the Alpha Legion, Night Lords, Iron Warriors and Word Bearers -- had already secretly turned to the service of Horus and Chaos. The three Loyalist Legions in the first wave of the assault are decimated during the battle that becomes known as the Drop Site Massacre. Loyalist and Traitor Space Marine Legions face each other in battles waged across the galaxy over the next 7 Terran years as Horus' Traitor forces drive on Terra itself.
 * ca. 212.M31 The Battle of Terra - The Warmaster Horus and all of his Traitor Legions of Chaos Space Marines lay siege to the Imperial Palace during the Battle of Terra in the greatest battle ever fought in Imperial history. The Emperor teleports aboard Horus' massive, fortress-like flagship in orbit of Terra after the Warmaster inexplicably leaves the vessel's Void Shields down, almost as an invitation to the final assault. The winged Primarch of the Blood Angels Legion, Sanguinius, once Horus' closest friend, is killed at the hands of the Warmaster. Horus is slain on the bridge of his Battle Barge the Vengeful Spirit by the Emperor of Mankind, who unleashes the full extent of his god-like psychic powers on Horus to literally extinguish his soul from the Warp so that his beloved son cannot be resurrected by their dark sorcery to serve as a puppet of the Ruinous Powers. However, the effort mortally wounds the Emperor, badly damaging his body, which on his orders is placed within the cybernetic sarcophagus and life-support system that is the Golden Throne. No longer able to personally direct the course of the Imperium of Man, its rulership is handed over to the Senatorum Imperialis of the High Lords of Terra, who will rule in the Emperor's name. Some time after the Battle of Terra, Terra becomes what would later be called a Hive World by the Imperium. Without the Emperor's guidance, the Imperium will soon become repressive, stagnant, bureaucratic and consumed by superstition and religious intolerance; all directly at odds with the rationalist and humanistic Imperial Truth promulgated by the Emperor during his lifetime.
 * ca. Early to Mid M31 - In the aftermath of the Horus Heresy, countless prophets and visionaries preach the Emperor is, and always has been, the one, true God of Mankind. The most influential of these cults of Emeperor-worship is the Temple of the Saviour Emperor, whose doctrine will eventually be adopted as the orthodox theology of the Imperial Cult centuries later.
 * ca. 212-218.M31 The Great Scouring - Traitor forces throughout the galaxy are quelled by the Imperial Loyalists of the Adeptus Astartes and the Imperial Army or forced to retreat from Imperial territory they captured under Horus' leadership in a campaign that becomes known to Imperial history as the Great Scouring. The Forces of Chaos, including the Chaos Space Marine Traitor Legions, Traitor Imperial Army units, the forces of the Dark Mechanicus and the Traitor Titan Legions, all retreat into the vast Warp rift called the Eye of Terror.
 * ca. M31 The Codex Astartes is completed - The Ultramarines Primarch Roboute Guilliman completes his Codex Astartes, a volume which lays down the new organizational and tactical doctrines for existing and future Loyalist Space Marine Chapters.
 * ca. Early M31 The Second Founding - The remaining Loyalist Space Marine Legions are broken into Chapters comprised of only 1,000 warriors each so that one man may never again command the full power of an entire Legion of Astartes. Twenty-three new Space Marine Chapters are created in this manner, whilst the 9 existing Loyalist Legions are reshaped into smaller Chapters that continue to bear the original names of their Legions. The Grey Knights, a special Space Marine Chapter comprised entirely of psykers that will eventually evolve into the Chamber Militant of the Ordo Malleus of the Inquisition, is secretly created by Malcador the Sigillite, the Regent of Terra and chief aide of the Emperor, on the moon of Saturn called Titan, which serves as the eventual headquarters for the Ordo Malleus, the branch of the Inquisition dedicated to protecting the people of the Imperium from the daemonic forces and temptations of Chaos. The newborn Inquisition takes as its eventual symbol Malcador's personal sigil.
 * ca. 284.M31 - The White Scars' Primarch Jaghatai Khan disappears while fighting several Kabals of the Dark Eldar on the world of Corusil V, near the Warp rift called the Maelstrom. Presumably he pursued a Dark Eldar Lord through an alien portal that led into portion of the Eldar Webway occupied by the Dark Eldar, perhaps even reaching their Dark City of Commorragh.
 * ca. 781.M31 The 1st Black Crusade Begins - The 1st Black Crusade is launched from the Eye of Terror by the new Warmaster of Chaos Undivided, Abaddon the Despoiler, Horus' heir as the leader of his former Legion the Sons of Horus, which renames itself the Black Legion following Horus' death. The First Battle of Cadia is waged for control of the Cadian Gate. The Forces of Chaos led by Abaddon are defeated and forced to retreat back into the Eye of Chaos.