Ultramarines - Age of Rebirth, M31-M33: In the aftermath of the Horus Heresy, it is the consummate strategist Roboute Guilliman, named lord commander of the Imperium and Imperial Regent by the consent of the other surviving Loyalist primarchs, who directed the majority of the counterattacks to drive back the traitorous Chaos forces. The Ultramarines primarch also oversaw the political and military reorganisation of the Imperium to learn and respond to the lessons of the Heresy, which included the Second Founding of the Adeptus Astartes into 1,000-warrior Chapters to ensure no treacherous commander could ever again unleash the full power of a Space Marine Legion; the division of the Imperial Army into the Astra Militarum and the Navis Imperialis to create an interservice rivalry that would constrain both forces, and the granting of autonomy to most of the Five Hundred Worlds of the Realm of Ultramar, which was reduced in size to a single sub-sector.The Ultramarines were the most numerous of the Loyalist Space Marine Legions at this time, with the others badly depleted, and Guilliman himself was everywhere, rallying the Imperial defenders and reinforcing them with his own augmented warriors before moving on to the next battle zone. Not once did the Space Marines take a step back, so strong was their faith in the Imperium, the Emperor and the Ultramarines primarch.Great Scouring (ca. 014.M31-Unknown Date.M31) - As one of the largest remaining Loyalist Legions that emerged relatively unscathed from the Horus Heresy, the Ultramarines played an instrumental part in the Great Scouring. This was the Imperium of Man's great counter-offensive against the Traitor Legions of the slain Warmaster Horus, following the end of the lamentable civil war after the Siege of Terra. Before actually being confined within the life support mechanisms of the Golden Throne, the Emperor had pronounced judgment on the Traitors: declared Excommunicate Traitoris, they were to be driven into the hellish region of the Warp rift called the Eye of Terror, which would hold them for all eternity. All records and memory of the Traitor Legions were to be expunged from Imperial archives. Worlds such as Isstvan V and Davin were scoured clean of all life because of their corruption by Chaos. The Traitor Legions' associated troops from the Dark Mechanicum or the regiments and starships of the Imperial Army that had turned to Chaos were to be destroyed or driven into the Eye. It would be as if the Traitor Legions had never existed to sully the Imperium with their betrayal. The fighting would continue for solar decades longer. The Loyalist Space Marine Legions destroyed at the Drop Site Massacre on Isstvan V were slowly reestablished using what little gene-seed the survivors had managed to escape with, though the Legions were refashioned as 1,000-Space Marine Chapters rather than full Legions as Primarch Roboute Guilliman's Codex Astartes now required after the Second Founding at the dawning of the 31st Millennium.Battle of Eskrador (Unknown Date.M31) - After the death of Horus at the end of the Horus Heresy during the Great Scouring, the Alpha Legion and the Ultramarines Legion met in battle on the world of Eskrador, where Roboute Guilliman faced his hated brother primarch Alpharius (unaware that it was actually his twin brother Omegon, who had assumed his twin brother's identity following Alpharius' death at the hands of Rogal Dorn during the Battle of Pluto) in bitterly contested close combat. Both struck one another in an instant, each power sword making a single stroke. For a second the two primarchs stood facing one another, than Alpharius slumped to the ground. Exalted by their primarch's victory the Ultramarines renewed their attack and cut down every last Alpha Legionary. But their exaltation was short-lived, as over the next few solar days the Ultramarines were harried from all sides by the Eskrador natives as well as remnants of Alpha Legionaries hiding throughout the mountains. After another solar week of futile combat against their shadowy opponents, Guilliman ordered his Ultramarines to evacuate the planet's surface. He then used his Legion's voidships to bombard the Traitors from orbit. Despite Guilliman's protests that he had no wish to fight such dishonourable foes, it seems hard to dispute the fact that the Ultramarines were soundly beaten by the Alpha Legion at every turn, despite the apparent loss of Alpharius.Creation of the Codex Astartes and the Second Founding (Unknown Date.M31) - Roboute Guilliman creates his magnum opus, the Codex Astartes, which will become the sacred tome of the new Adeptus Astartes' military organisation, strategy and tactics. The long process of breaking up the Loyalist Space Marine Legions into individual 1,000-warrior Chapters takes many Terran years to be fully enacted. So begins what is remembered by historitors as the "Second Founding."Green Hordes of Talassar (Unknown Date.M31) - A great horde of Orks ravage Talassar, threatening to utterly destroy civilisation upon the Ultramarian world's single continent of Glaudor. Testing his Codex Astartes, Guilliman deploys his army with minimal direct guidance. His forces follow protocol with a series of rapid strikes that lead to victory.Castigation of Colchis (ca. 032.M31) - Following the end of the Horus Heresy, the Imperium launched a massive retribution crusade, known as the "Great Scouring," to drive out the remaining Traitor Legions and those forces still loyal to them. Following this period of bloody vengeance and violence, around 032.M31 the Ultramarines finally took the fight to the Word Bearers' Legion homeworld of Colchis, in retribution for what the Word Bearers had done to Calth during the early years of the Horus Heresy. When they arrived they found a devastated world, its industry in ruins and its people clinging desperately to civilisation. Given Lorgar's treachery and the Imperium's fear that his Chaos taint had spread throughout the population who had converted to the Word Bearers' heretical faith in the Ruinous Powers, the newly-formed Inquisition ordered the planet to undergo Exterminatus, and following a planetary assault, the Ultramarines' battle barge Octavius bombarded Colchis with Cyclonic Torpedoes. The geological structure of Colchis was highly unstable and the resultant seismic activity caused by the torpedoes' detonations split the planet apart. Nothing now remains of Colchis and where it once existed in the galaxy is still a closely guarded secret of the Inquisition.Battle of Thessala (121.M32) - Roboute Guilliman continued to serve with the Ultramarines Chapter and its successors after the Heresy, leading them for another standard century after the Second Founding well into the campaigns of the Great Scouring. It was Guilliman's actions subsequent to the Horus Heresy that made him the figure of adoration for the people of the Imperium that he would become. With the Traitors scattered and the Emperor to all intents and purposes lost to Humanity, the Imperium stood at the precipice. It was the genius and leadership of Roboute Guilliman that saw the Imperium through its first century after the Heresy, as he kept invaders at bay and saved the scattered worlds of Humanity from collapsing into utter anarchy once more. Yet the primarch of the Ultramarines was dealt a mortal wound by his traitorous brother Fulgrim, primarch of the Emperor's Children, during the Battle of Thessala. The monstrously serpentine Fulgrim, gifted with great powers by his patron Chaos God Slaanesh and elevated to the status of Daemon Prince, stabbed Guilliman in the neck with one of his many poisoned blades. The loss of their primarch was crushing to the Ultramarines, who bore their gene-father away from battle and interred him inside a stasis field in the centremost temple within the Fortress of Hera upon Macragge. There he remained for over ten thousand Terran years, until he returned on the eve of the Great Rift's birth to defend the Imperium he strove so hard to build.Reunited (646.M32) - A one-hundred-standard-year period of anarchy in the wake of the War of the Beast and The Beheading was ended by the intervention of the Space Marines. Agnathio, Chapter Master of the Ultramarines, united over fifty Chapters of the Adeptus Astartes and arrived upon Terra. Agnathio held a locked council with the squabbling noble "rulers" of Terra. What was said has never come to light, but when the Space Marine fleets returned to their homeworlds, there once again sat twelve High Lords of Terra on the Senatorum Imperialis, and unity was restored to the Imperium.