833.M30 Osiris Rebellion - For unknown reasons, the eleven star systems of the Osiris Cluster declared independence from the Imperium. The XIII Legion sent its 12th Expeditionary Fleet to put down the rebellion. But failures in intelligence turn what was intended to be a swift victory into a battle for attrition against a previously unknown xenos threat -- Osiran Psybrid xenoforms. The vile aliens drive the human population to attack the Legiones Astartes in droves. Ordering his force to withdraw after sustaining heavy losses, Legion Commander Gren Vosotho, along with the XIII Legion flagship Sethaln's Thunder, is lost. Command falls to First Captain Marius Gage. The Osiris Cluster is then blockaded. The 12th Expeditionary Fleet returns a standard year later with a force heavily augmented from the Solar Armada, elements of the XVIII Legion and specialist anti-psyker cadres from Terra. To their surprise, they discover the worlds of the Osiris Cluster have either been left as wastelands of unburied dead or are now locked in turmoil and civil strife.
835.M30 Discovery of Rogal Dorn - The Great Crusade reaches the Inwit Cluster, a collection of Ice Worlds ruled by the Primarch Rogal Dorn. The lost primarch, the seventh to be rediscovered, greets the Emperor on the bridge of the Phalanx, a colossal reactivated starship dating back to the time of the Age of Technology, and submits to his authority. The Emperor quickly instructs Dorn in the ways of the Imperium and their objectives with the Great Crusade, and soon passes off command of the VII Legion, whom Dorn remakes into the Imperial Fists. The primarch transfers their headquarters to the Phalanx.
837.M30 Discovery of Roboute Guilliman - Raised on the world of Macragge by a noble consul, the Primarch Roboute Guilliman grows into a prodigal leader. The Emperor's arrival is delayed for years by Warp Storms -- by the time He arrives, the primarch rules a stellar empire known as the Realm of Ultramar, the "Five Hundred Worlds." Impressed with His son's superlative organisational skills and strategic planning, the Emperor quickly passes on command of the XIII Legion to Guilliman, who reforges them into his own, as the newly renamed Ultramarines.
840.M31 Discovery of Magnus the Red - A strong Warp presence is detected on the remote world of Prospero, leading the Emperor to investigate. There He finds Magnus the Red, the most psychically gifted of his sons, and embraces him as commander of the XV Legion, the Thousand Sons. Magnus learns much from the Emperor's psychic might in the following years.
842-843.M30 Liberation of Incaladion - During the liberation of the war-torn Forge World of Incaladion, the IV Legion displayed its reliance on rationality and intellect set against infrequent but telling episodes of bloody-minded stubbornness in the face of overwhelming odds. In a gruelling solar-year-long campaign, victory was at last achieved, but the war saw the near-annihilation of the IV Legion's 8th Expeditionary Fleet's frontline forces in what was arguably a needlessly costly fashion.
843.M30 Discovery of Xana II - A damaged galleass belonging to the Rogue Trader Casilida DeAniasie, having been flung far off-course after engaging in battle with Fra'al corsairs, intercepted a trio of hulking automata warships at the edge of the intergalactic void. Although they might have taken or destroyed her already damaged starship with little effort, these vessels instead offered aid and carried with them a message of greeting and an offer of diplomatic exchange between the "Sovereign Forge Domain of Xana" and the Imperium of Man and its Emperor.
843.M30 Discovery of Sanguinius - Borne by the currents of the Warp to a moon scorched by radiation from an ancient thermonuclear war, Sanguinius possesses magnificent, angelic wings and psychic foresight. He thus foresees the arrival of the Emperor, and pledges himself to the Imperium in exchange for the safety of Baal's rad-scarred and pious people. Not long after their reunion, Sanguinius is given command of the IX Legion and remakes them in his own image, renaming them the Blood Angels.
846.M30 Discovery of Lion El'Jonson - Forward scouts of the Great Crussade encounter the Death World of Caliban, and the knightly orders that protect it from Warp-spawned beasts. Their leader, Lion El'Jonson, is found to be one of the lost primarchs, and assumes command of the I Legion upon meeting the Emperor -- later renaming them the Dark Angels after an alleogircal figure of Calibanite myth from his youth. A young, newly-inducted Calibanite I Legion Librarian, Zahariel El'Zurias narrowly averts an attempted assassination on the Emperor's life soon after His arrival.
848.M30 Suppression of Sarosh - The Human-settled world of Sarosh, ruled by a massive planetary bureaucracy and originally discovered by the White Scars, had initially appeared eager to join the Imperium and embrace the Imperial Truth. Yet after over a standard year of Imperial rule under its Planetary Governor Harlad Furst, its native leadership had failed to meet any of the benchmarks of Compliance. Its leaders explained to Furst that the world's large bureaucracy made the movement towards Compliance slow and difficult. To speed up the effort, the Dark Angels took over Compliance duties for Sarosh from the White Scars. After an assassination attempt on the Dark Angels Primarch Lion El'Jonson by the Sarosi leader known as the Lord High Exacter aboard El'Jonson's flagship the Invincible Reason using a hidden nucleonic device, it is discovered that the Sarosi bureaucracy system is a cover for a cult supposedly communing with xenos entities from an alternate dimension, most likely the the Warp. The Dark Angels and forces from the 4th Expeditionary Fleet eliminate all traces of the cult and bring the world into Imperial Compliance after a short but savage campaign. Editor's Note: This date is likely incorrect, as later sources place the Lion's arrival on Sarosh sometime after the end of at least the Second Rangdan Xenocide, which did not begin until 863.M30. As such, this event most likely took place in the late 9th century of M30.
849.M30 Discovery of Perturabo - A scientific and military genius on the world of Olympia draws the Emperor's attention, found to be his lost son, the Primarch Perturabo. The bitter and analytical primarch judges the IV Legion's war record to that point in the Great Crusade harshly, and orders their decimation -- execution of one in every ten Legionaries -- as punishment. Drawing lots, one in nine IV Legion Astartes are killed by their remaining battle-brothers with their bare hands. Following this action, Perturabo leads his Legion to the Meratara Cluster and forges them into a Legion in his own image. The IV Legion formally becomes known as the Iron Warriors.
849.M30 Fall of the Black Judges - This was the Iron Warriors' first Imperial Compliance campaign under the direct command of their primarch, which was conducted against the barren, ravine-hollowed moon known as the "Rock of Judgement" and its masters, the heretical Black Judges. These self-appointed arbiters of Human purity, life and death, were twisted and withered creatures that had once been human in ages past. The IV Legion, reeling from its enforced "decimation" as punishment at its new master's hands, was shamed into a desperate desire to prove itself to its primarch, and it was the Black Judges that were to suffer its pent-up hatred and wrath. By Perturabo's design the enemy was crushed without mercy and their domains were stripped of every valuable resource and technology; wreckage and weapons flowed to Olympia and the Black Judges' long-guarded secrets fell also to the newly renamed Iron Warriors and their master, as well as to the Mechanicum in return for their aid. With the world stripped of its resources, the orbital shipyards of the Rock of Judgement were finally set in orbit afresh around Olympia and set to work fashioning a new generation of warships under Perturabo's seal.
ca. 850s.M30 Pacification of Schravaan - This was a joint Imperial Compliance action conducted by four Legions of Space Marines against the xenos known as the Badoon. Upon the Badoon's homeworld of Schravaan, the Iron Warriors won a great victory when they stormed the final refuge of the species. They breached the defences and held their position while the other Legions carried the city beyond. During the following victory feast, Horus proclaimed Perturabo the greatest master of siege warfare in the Great Crusade. Fulgrim then inquired of his brother Rogal Dorn whether he thought even the defences of the Imperial Palace, which Dorn had crafted, could resist the Iron Warriors, to which Dorn replied that he regarded those defences as being proof against any assault if well-planned. Upon hearing what he took to be a slight upon his skill, Perturabo flew into a rage and unleashed unfounded accusations against his brother. After this incident, the two rarely spoke, and neither of their Legions served in the same campaign for the remainder of the Great Crusade.