4th Founding

The 4th Founding of the Adeptus Astartes occurred nearly a hundred years later, around 646.M32, following the climax of the catastrophic event known as The Beheading, in which the Grand Master of Assassins, Drakan Vangorich, deployed his elite assassins of the Officio Assassinorum, and the High Lords of Terra were slain to a man in 546.M32. Afterwords the Imperium descended into a period of anarchy. Nearly a century later, it was only through the direct intervention of Chapter Master Agnathio of the Ultramarines and fifty other Chapters Master arrival upon Terra to contain the anarchy, did the political squabbling finally cease, and when they departed, twelve new High Lords of Terra had been chosen. They more than likely authorised the 4th Founding of Space Marine Chapters to help bring order to an Imperium rife with civil discourse and insurrection, and to restore the rule of Imperial law.