Second Founding - History: When the surviving Space Marine Legions were divided into Chapters seven years after the Horus Heresy in 021.M31, a new tier of the Adeptus Astartes was created. This event became known as the "Second Founding," during which each of the Second Founding Chapters was created from the ranks of the parent (sometimes referred to as the "Progenitor") Legion.As such, the first warriors to form the ranks of the new Chapters were the very same Space Marines who had fought at the side of their primarch before and during the tumultuous Horus Heresy.Each Second Founding Chapter initially shared their parent Legion's gene-seed -- subsequently each Chapter's gene-seed was isolated by the Adeptus Mechanicus, forming new genetic lines. Because the Space Marines that made up each of the Second Founding Chapters originated from one of the Legions that first served the Emperor, the Chapters that were created were called "Successor Chapters," a title not given to later Chapters of the many subsequent Foundings that have been carried out by the Imperium after that initial split to keep the number of extant Chapters at around 1,000.In some cases, the Chapter was created by the amalgamation of battle-brothers of a particular outlook. Such was the case when the Imperial Fists Legion was broken down into the Black Templars and the Crimson Fists Chapters. Many of the more zealous "old Legion" battle-brothers joined the Black Templars Chapter, while those more willing to follow the doctrines of Roboute Guilliman's Codex Astartes forming the basis of the Crimson Fists Chapter.As time marched on and these original Legionaries passed into memory, the Second Founding Chapters forged their own histories and traditions distinct from their Progenitors. Whatever path they took, however, the new Chapters remained rightly proud of their roots and even many thousands of Terran years after the Second Founding they are held as second only to the First Founding Chapters in the honour afforded to them.Many Second Founding Chapters retain close links with their Progenitor First Founding Chapter, and this is especially true amongst the successors of the Ultramarines, who are known as the "Primogenitor Chapters," meaning "first born." On countless occasions, the Ultramarines' successors have stood side by side with their parent Chapter.While no strict or formalised superiority exists, they often look to the Ultramarines' Chapter Master Marneus Calgar as a unifying figurehead, following his lead and prosecuting his wars. Over the ten thousand years of the Imperium's history some Second Founding Chapters have clashed with their parent Chapter, striking out on their own for a myriad of reasons.The vast majority of the Second Founding Chapters were created from the ranks of the Ultramarines Legion, which had always been the largest and therefore capable of being divided in numerous Chapters. Other Legions were not large enough to be divided more than once, as was the case with the Space Wolves and their Successor Chapter, the ill-fated Wolf Brothers.The Second Founding occurred so long ago in the Imperium's troubled history that no reliable accounts of its details exist. Exactly how many Chapters were founded and from which Legions is unclear. One of the earliest known accounts is to be found within a version of the Codex Astartes known as the Apocrypha of Skaros, and this crumbling tome claims that the Ultramarines Legion sired twenty-three Primogenitor Chapters, but famously omitted to list them all.Furthermore, no version of the codex lists a Second Founding as having been raised from the Salamanders Legion, though this does not mean that none ever were. It is possible that the Raptors, the Silver Skulls and other Chapters were also established during the Second Founding.The Grey Knights, the elite Space Marine Chapter that serves as the Chamber Militant of the Ordo Malleus of the Inquisition, was secretly created at the end of the Horus Heresy, the source of its gene-seed unknown but believed to have been derived from the Emperor Himself rather than any Primarch.Due to the scarcity of information regarding the identity and status of the Second Founding Chapters, a huge amount of mystery and legend surrounds many of them. Some have appeared in the annals of the Imperium's history in name only, their deeds and fates unknown to all but the immortal Emperor. Others have a glorious history, yet have not been heard from in centuries.The status of some Chapters as Second Founding is disputed by especially learned historitors and savants, though never in the presence of the subject. Some Chapters that believe themselves Second Founding may not be at all, while others may be Second Founding but be ignorant of the fact.The ten thousand year history of the Imperium is so fractured, its annals so scattered and incomplete, that it is likely that the full truth of the matter may never be known.