Space Marines - The Second Founding: The Second Founding of the Space Marines was decreed seven Terran years after the death of Horus. The existing Space Marine Legions were broken down and re-founded as smaller, more flexible formations.Where the old Legions were unlimited in size, the new formations were fixed at approximately 1,000 Astartes. This corresponded to the existing Astartes unit within some Legions called the "Chapter," and in future the Chapter was recognised as the standard autonomous Space Marine formation.No longer would one man have power over a force as powerful as a Space Marine Legion. The existing Space Marine Legions were divided into new Chapters. One Chapter kept the name, badge and colours of the original Legion, while the remaining Chapters took on new titles, badges and colours.Most of the old Legions were divided into fewer than five Chapters, but the Ultramarines, being by far the largest of the Legions, were divided many times.The exact number of new Chapters created from the Ultramarines is uncertain: the number listed in the oldest known copy of the Codex Astartes (the so-called Apocrypha of Skaros) gives the total as 23, but does not name them.As a result of the Second Founding, the Ultramarines' gene-seed became the favoured genetic stock of most subsequent Astartes Foundings.The new Chapters created from the Ultramarines are often referred to as the "Primogenitors," or the "first born." All of the Primogenitor Chapters venerate Roboute Guilliman as their founding father and patron.The Codex Astartes further defines the tactical roles, equipment specifications, and uniform identification markings of the Space Marines.Some of its contents seem petty and restrictive, hardly worthy of the great mind of a primarch. Others describe actual battles together with comments on the tactics employed and the decisions of the commanders of the day.As such, the Codex is revered as a holy text of the Imperial Cult, and many Chapters regard its recommendations as sanctified by the Emperor Himself.The Chapters that rigidly follow the word of the Codex Astartes are sometimes referred to as "Codex Chapters" or Codex Astartes-compliant Chapters. These Space Marines adhere to the Codex as the model for their organisation, identification markings and tactical doctrine. Of all of the Codex Chapters, the most famous is the Ultramarines, the Chapter of Roboute Guilliman himself.The Adeptus Terra has never decreed it necessary to enforce the Codex absolutely. Indeed, it is doubtful whether it could if it so chose. However, with subsequent Foundings, they have always favoured the Ultramarines' gene-seed and created many new Codex Chapters from that genetic line.With the passage of time, some of these Chapters have subsequently strayed from the strict letter of the Codex, introducing new variations on their organisation or tactical doctrine but remaining broadly faithful to the principles laid down by Roboute Guilliman many millennia before.The history of the Imperium since the Horus Heresy is not a continuous story. There have been periods of rebellion and anarchy, times when the balance of power has suddenly changed and history has quite literally been rewritten.Many of the subsequent Foundings of Space Marine Chapters belong to these troubled times, making it almost impossible to ascertain when some Chapters have been created.It is believed that of the one thousand or more Chapters thought to be in existence today, more than a third are descended from the Ultramarines, either directly or through one of their Primogenitor Chapters of the Second Founding.It is not known how many new Chapters were created by the Second Founding. Many records were lost during the Age of Apostasy, a troubled time in the 36th Millennium that bestrides the history of the Imperium like an impenetrable wall. In all likelihood, some of the Chapters created during the Second Founding have since been destroyed, leaving no records of the deeds.Others have been lost in more recent times, and their names are now all that remains of them.