Roboute Guilliman - Imperial Reform: The Loyalist Space Marine Legions had lost tens of thousands of troops during the fighting of the Heresy, and half of the original 18 Legions had sided with Horus and been corrupted by Chaos. As a result, the number of Astartes left to the Imperium after the end of the Heresy was very few, yet never were they more needed.The confusion and disorder following the Horus Heresy had left the Imperium weak and vulnerable. Everywhere the enemies of Humanity prepared to attack. Many worlds remained in the grip of Chaos.Into this breach stepped Roboute Guilliman and the Ultramarines. Always the largest of the Astartes Legions since the middle years of the Great Crusade, the Ultramarines found themselves divided and dispatched all over the Imperium in a desperate effort to stem the tide of invasion and unrest.Guilliman, ever the statesman, took over control of the Council of Terra, establishing the position and authority of the Lord Commander of the Imperium. In this role, he guided the Imperium forward after the internment of the Emperor in the Golden Throne for over a Terran century, through the long hard days of the Great Scouring when the Imperium reclaimed and cleansed the worlds lost to the Traitors and reestablished Imperial rule across the galaxy.The Ultramarines successfully held the Imperium together during a time of intense danger. Macragge was able to supply new recruits at such a rate that before long the Ultramarines alone accounted for more than half the total number of Space Marines, and few were the star systems where their heroism went unnoticed. Within decades, order was restored to the Imperium.After decades of intense fighting, stability was restored. To prevent a single commander having as many superhuman Astartes at his command as Horus had, Guilliman reformulated the sizes of all of the Loyalist Space Marine Legions into thousand-man Chapters, breaking apart the 9 original Loyalist First Founding Legions into the much smaller Second Founding Chapters.Never again would one person, no matter how noble and unblemished their motives, wield the power of an entire Space Marine Legion. At the same time, Guilliman had been hard at work for decades on a new method for waging war that finally reached its fruition after the Horus Heresy.The rationale and proper organisation of Space Marine Chapters are the main topic in this masterwork of military strategy, the Codex Astartes.Its doctrines would reshape the future of all Space Marines and forevermore dictate the foundation for the Imperium's military strength and the ultimate survival of Mankind.The Second Founding of the Space Marines was decreed seven Terran years after the death of Horus and the end of his Heresy. Most of the old Loyalist Legions divided into fewer than 5 Successor Chapters, but the Ultramarines were divided many times.The exact number of Successor Chapters created from the Ultramarines is uncertain: the number listed in the oldest copy of the Codex Astartes gives the total as 23, but does not name them. With the Second Founding, the size of the Ultramarines force was much reduced. Most of the Space Marines left Macragge to establish new Chapters elsewhere.The Ultramarines' fortress-monastery on Macragge, the Fortress of Hera, had been built to accommodate more than ten times as many Space Marines as now remained on their homeworld. As a result, its arsenals and weapon shops were partially dismantled and taken by the new Chapters to found their own bases. The genetic banks of the Ultramarines, and the huge recruitment organisation, were similarly reduced.As a result of the Second Founding, the Ultramarines' gene-seed became pre-eminent across the Imperium. The new Chapters created from the Ultramarines during the Second Founding are often referred to as the "Primogenitors," or "first-born." The lasting heritage of Guilliman was not only genetic, but spiritual.Even to this day, 10,000 standard years later, all the Primogenitor Chapters venerate Roboute Guilliman as their own founding father and patron, and hold the ruler of Ultramar, whoever he be, as the exemplar of all that it means to be a Space Marine. So did the Ultramarines rise to become preeminent amongst their brother Chapters.