When the surviving Space Marines Legions were divided into Chapters seven years after the Horus Heresy, a new tier of the Adaptus Astartes was created at the order of the High Lord of Terra. This event became known as the "Second Founding", during which each of the Second Founding Chapters was created from the ranks of the parent (referred to as the "Progenitor") Legion. As such, the first warriors to form the ranks of the new Chapters were the very same Space Marine who had fought at the side of their Primarch before and during the tumultuous Horus Heresy. The mobilization of vast resources was ordered by the Adaptus Mechanicus who play the essential role in the process of testing and developing the gene-seed samples that would provide the basis of the new Chapters. Entire forge worlds were turned to the manufacture of the mighty arsenal of weaponry, ammunition, armor, vehicles and war ships that any such force required. As time marched on and these original Legionnaires 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 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. 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. In some cases, the Chapter was created by the amalgamation of Battle-Brothers of a particular stance.
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 received glorious history, yet have not been heard from in centuries. The ten thousand year history of the Imperium is so fractured, its annals so scattered and incomplete, that it is likely that the truth of the matter may never be known.
From Deathwatch Origins
