Horus Heresy - Great Crusade: When the great Warp Storms that had cut off Terra since the end of the Dark Age of Technology subsided, and the Age of Strife came to an end at the dawn of the 31st Millennium, the Emperor of Mankind deemed it time to begin his Great Crusade, a massive campaign to conquer the galaxy by which he and his armies would free all human-settled colony worlds from alien oppression or primitive ignorance and reunite the human race across the galaxy under the single banner of the new Imperium of Man. To execute this plan, the Emperor created the primarchs, his god-like, genetically-engineered superhuman offspring.The primarchs were still in their infancy, growing to hyper-accelerated maturity in their special gestation tanks, when they were snatched away from the genetic laboratory deep beneath the Himalazian (Himalayan) Mountains on Terra where they had been created and gestated by the Emperor using His own DNA. The cause of this disappearance was the Chaos Gods, who were fearful that with the primarchs, the Emperor would be able to impose His new order across the galaxy and weaken their own firm grip on the collective unconsciousness of the minds of Humanity, which was the source of both their existence and the growth in their power within the Immaterium.Uniting their powers under the leadership of Tzeentch, the Dark Gods opened a portal from the Warp and broke into the laboratory where the primarchs were gestating through the potent psychic wards the Emperor had erected. Unable to destroy the primarchs outright because of the protections the Emperor had laid upon them, the Chaos Gods instead chose to scatter them across the galaxy through the Warp.The superhuman infants eventually came to rest on diverse, human-inhabited worlds. It was at this time that the Ruinous Powers first touched the souls of those primarchs who would eventually turn to the worship of Chaos, infecting them with a shard of corruption.Certainly the fact that each of the primarchs was ultimately cast ashore on an inhabited human world was no accident; the Chaos Gods may have hoped that by having the primarchs raised among Humanity without the direct guidance of the Emperor as they grew they would display more of the human weaknesses that would make them easier to corrupt when the time came.During the course of the Great Crusade, the Emperor encountered each of the primarchs on their scattered homeworlds in turn. To fill the gap in His military plans for the Great Crusade wrought by the primarchs' absence after they had been stolen away, the Emperor had instead created 20 Space Marine Legions, several of which, such as the [[Ist Legion]], had been raised even as the Unifications Wars still raged.The Emperor used the primarchs' individual genetic material still in His possession to craft the genetically-enhanced transhuman warriors of each of the Legiones Astartes, creating 19 gene-seed organs that could be implanted within an adolescent Human male to transform him into a Space Marine. After the Emperor rediscovered His sons scattered across the galaxy, He deemed it fitting that each primarch should lead their genetic offspring as the master of the Legion whose Astartes bore their DNA.However, in time this decision would prove a critical mistake, as the Space Marine gene-seed creation process made the Emperor, the primarchs and the Space Marines analogous to grandfather, fathers and sons, respectively, in their genetic inheritance and superhuman abilities.In time, many of the Space Marines in the Legions, especially those recruited from their primarchs' homeworld rather than from Terra before the primarchs' rediscovery, would come to venerate and feel more loyalty for their primarch than the Emperor of Mankind.