13th Founding

The Thirteenth Founding, which occurred sometime between the 35th and 36th Millennia, is one of the very rare foundings of Space Marine Chapters that occurred that were not recorded in exact detail. Since the Horus Heresy, the Adeptus Terra has maintained a bank of original gene-seed from every single Chapter ever created, with one notable exception: the Thirteenth Founding, also known as the Dark Founding. There is no reliable records that indicate how many Chapters were created during the Dark Founding or what became of them. Full disclosure of the exact of the exact details of this mysterious founding may lie deep in some within the record office of the Adeptus Terra. There are only two known Chapters that have been acknowledged as being created during this period in Imperial history - the mysterious Exorcists and the Death Spectres Chapters.

The Exorcists were founded as part of a highly-classified Imperial experiment to create Space Marines who were unusually resistant to daemonic possession and Chaotic corruption because as part of their initiation into the Chapter they had actually been forced to serve as daemonhosts for a short time before having the creature expelled back to the Warp by the intervention of an Inquisitor. The Death Spectres are the only second known Chapter of Astartes, besides the Exorcists, to have been created in this unusual Founding. They are possibly a Successor Chapter of the Raven Guard as they share the same mutations as found in that Chapter's gene-seed.