- "In their veins pumps the blood of Primarchs..."
- — High Lord Amalthid
The Second Founding of the Space Marines occurred seven standard years after the end of the Horus Heresy, in the early 31st Millennium. This Founding involved the division of the existing Loyalist Space Marine Legions into the far smaller, 1,000-man autonomous Chapters of the Space Marines as decreed by the new Codex Astartes, written by the Ultramarines' Primarch, Roboute Guilliman. The remaining Loyalist Space Marine Legions were divided into smaller Successor Chapters -- one Chapter maintained their parent Legion's original name, badge and colours, while the remaining Chapters took new names and heraldry.
- "Roboute Guilliman. Guilliman the tactician. Guilliman the warrior. History will remember the Primarch of the Ultramarines by many titles. To us of the Blood he will have only one -- Guilliman the butcher. With law and edict, Guilliman ripped the heart from the Legions. Even his own sons were not spared his treachery. Where Horus had sought to use a hammer blow, Guilliman used a duellist's blade. In the end, the result was the same. Brother became cousin. Cousin became exile. Guilliman's new chapter, his new beginning, was a sundering to all that had come before. Stripped of honour and tithe, of history and deed, we were all of us undone. Bastards of war and victory, we were Angels no more."
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 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, 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. The Grey Knights, the elite Space Marine Chapter that serves as the Chamber Militant of the Ordo Malleus of the Inquisition, was secretly created during the Second Founding, the source of its gene-seed unknown. It is possible that the Raptors, the Silver Skulls and other Chapters were also established during the Second Founding.
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 truth of the matter may never be known.
Select Second Founding Successor Chapters
|Angels of Absolution||Dark Angels||I||Unknown|
|Angels of Redemption||Dark Angels||I||Unknown|
|Angels of Vengeance||Dark Angels||I||Unknown|
|Angels of Vigilance (Suspected, unconfirmed)||Dark Angels||I||Unknown|
|Lions Sable (Destroyed and Forgotten)||Dark Angels||I||Unknown|
|Storm Lords||White Scars||V||Unknown|
|Wolf Brothers||Space Wolves||VI||Beor Arjac Grimmaesson|
|Black Templars||Imperial Fists||VII||Sigismund|
|Crimson Fists||Imperial Fists||VII||Alexis Polux|
|Excoriators||Imperial Fists||VII||Demetrius Katafalque|
|Fists Exemplar||Imperial Fists||VII||Oriax Dantalion|
|Iron Knights||Imperial Fists||VII||Unknown|
|Soul Drinkers (Excommunicate Traitoris)||Imperial Fists||VII||Unknown|
|Angels Encarmine||Blood Angels||IX||Unknown|
|Angels Sanguine||Blood Angels||IX||Unknown|
|Angels Vermillion||Blood Angels||IX||Unknown|
|Blood Drinkers||Blood Angels||IX||Unknown|
|Flesh Tearers||Blood Angels||IX||Nassir Amit|
|Sons of Sanguinius||Blood Angels||IX||Unknown|
|Brazen Claws||Iron Hands||X||Unknown|
|Emperor's Shadows||Iron Hands||X||Unknown|
|Red Talons||Iron Hands||X||Autek Mor|
|Black Consuls||Ultramarines||XIII||Arrias Cordos|
|Doom Eagles||Ultramarines||XIII||Tulian Aquila|
|Patriarchs of Ulixis||Ultramarines||XIII||Unknown|
|Praetors of Orpheus||Ultramarines||XIII||Unknown|
|Black Guard||Raven Guard||XIX||Unknown|
- Citadel Journal #20, "Creating a Space Marine Chapter - The Sons of Sanguinius," by Isaac Tobin, pp. 19-20
- Codex: Angels of Death (2nd Edition), pg. 7
- Codex: Black Templars (4th Edition), pg. 6
- Codex: Blood Angels (5th Edition), pg. 54
- Codex: Blood Angels (3rd Edition)
- Codex: Dark Angels (5th Edition), pp. 10, 73-75
- Codex: Dark Angels (3rd Edition, 2nd Release)
- Codex: Dark Angels (3rd Edition), pg. 14
- Codex: Space Marines (7th Edition) (Digital Edition), pp. 12-15, 26-27, 109-110, 114-116, 136-143
- Codex: Space Marines (5th Edition), pp. 7-8
- Codex: Space Marines (4th Edition), pp. 22-47
- Codex: Space Wolves (5th Edition), pg. 9
- Codex: Space Wolves (2nd Edition), pg. 9
- Codex: Ultramarines (2nd Edition), pp. 9-10
- Dataslate: Cypher - Lord of the Fallen, pp. 15, 17-18, 20-22, 28
- Deathwatch: Honour the Chapter (RPG), pp. 9-16, 58-88, 103-105, 106, 109, 111
- Deathwatch: Rites of Battle (RPG), pp. 53, 55-58, 60-64, 66
- Index Astartes I, "Codex Astartes: The Holy Tome of the Space Marines," by Rick Priestley & Andy Chambers, pp. 12-13
- Warhammer 40K Compendium (1st Edition), pg. 34
- White Dwarf 287 (UK), "Horus Heresy: Sabertooth CCG," pg. 86
- White Dwarf 258 (UK), "Index Astartes First Founding: Wolves of Fenris"
- White Dwarf 248 (UK), "Index Astartes First Founding: Promethean Warriors - The Salamanders Space Marine Chapter," pg. 76
- White Dwarf 177 (UK), "Golden Demon Space Marine Chapter Design Competition", pg. 30
- Age of Darkness (Anthology) edited by Christian Dunn, "Rules of Engagement" by Graham McNeill
- Battle of the Fang (Novel) by Chris Wraight
- Calgar's Fury (Novel) by Paul Kearny
- Farsight: Crisis of Faith (Novel) by Phil Kelly
- Legion of the Damned (Novel) by Rob Sanders
- I Am Slaughter (Novel) by Dan Abnett
- Storm of Damocles (Novel) by Justin D. Hill
- The Lives of Ferag Lion-Wolf (Short Story) by Barrington J. Bayley