Nikaea

Nikaea is a planet widely known in Imperial history as the site of the Council of Nikaea on which the Emperor of Mankind and his Primarchs met during the Great Crusade to decide the fate of psykers and the use of psychic powers or "sorcery" within the Imperium of Man. Ultimately the use of psykers was allowed but tightly restricted, while the potent and unrestricted use of psychic abilities that was defined as sorcery was officially banned. The psychically powerful Primarch Magnus the Red and his Space Marine Legion the Thousand Sons would continue to study such powers in secret on their homeworld of Prospero. The term "Council of Nikea" is a historical reference to the Christian Church's Council of Nicaea, which occurred in the year 325 AD and determined the content of orthody Christian belief as laid out in the Nicean Creed.

Council of Nikaea
There was an increasing concern as the Great Crusade progressed forth considering the use of Sorcery. More and more often the Imperial Army and Space Marines would make planet fall only to find that the populace thralls to mysterious powers. These people were essentially slave cults who would resist the forces of the Emperor with sorcerous powers granted them by daemonic beings from across the Warp. Powers that were very akin to those used by the Thousand Sons of Magnus. Mortarion who knew by his own personal experience the dangers of the Warp, and Leman Russ for whom any battle fought through sleight of hand and clever deceit was by definition dishonorable, highly criticized the Thousand Sons. The schism grew so great that it threatened the very stability of the fledgling Empire and so the Emperor himself decreed a council to resolve the issue once and for all.

The Debate
Both sides of the debate were gathered to the planet Nikaea to give their views, with the Emperor as an arbiter, enthroned above the dais in an ancient amphitheater that seated tens of thousands. On one side: Witch hunters presented their case reciting a litany of human suffering inflicted upon the Emperor's own subjects by sorcerers enslaved by Chaos, of gibbering mutants who had lost all humanity, and of cults and power hungry men who turned their psychic gifts to dark purposes. On the other: Magnus himself. His very presence frightened many, but he began to speak with great charisma. His argument was that no knowledge was tainted of itself, and no pursuit of knowledge was never wrong so long as the seeker of that truth was master of what he learned. He spoke with finality that the Thousand Sons had mastered their knowledge and that there was no ways too labyrinthine for them to know.

Judgment
Magnus had spoken passionately with great power and the Council became even more divided. While they had strong arguments in their favour to justify their anti-psyker position, the Witch Hunters could not effectively match Magnus' persuasiveness. The tension could easily have been cut with a knife when a group of Space Marine Librarians approached the Dais. The Emperor acknowledged them with a nod, and all fell silent. Among the group were some of the greatest Librarians of the Space Marine Legions. They formed a semi-circle around the Dais to indicate that they spoke as one voice, but it was a young Epistolary who spoke. A psyker, he proposed, was like an athlete, a gifted individual whose native talent must be carefully nurtured. Psykers were not evil in themselves. Sorcery, however, was a knowledge of how to wield psychic powers that had to be sought for, even bargained for with the foul entities of the Warp. No one could be sure who benefited in the deal. The Librarians proposed that all psykers be strictly educated by the Imperium with the express purpose of using their abilities to serve Mankind. This should become an immediate Imperial priority.The practice of psychic Sorcery would forever be outlawed as an unforgivable offense against Mankind and the worst kind of heresy. The end result of the Council of Nikaea's deliberations was a compromise that offered both the pro-and-anti-psyker factions something. This compromise appealed to the Emperor, and he declared it to be law immediately without allowing any rebuttal from either side. The Edicts of Nikaea stood for the next 10,000 standard years as the Imperial policy regarding human psychic mutation. The Edicts also created a new position among the Space Marine Legions, the Space Marine Chaplain, who was intended to help the Astartes remain true to both the Imperial Truth and the Emperor's commands and policies. Magnus attempted to storm out of the hall in protest, but was barred by the Emperor himself. The confrontation between father and son is recorded in the Grimore Hereticus. The Emperor ordered Magnus to cease the practice of sorcery and incantation, and the pursuit of all knowledge related to magic. Magnus of course did not like the idea, and it was said his face was brittle enough to crack. But in the end he bent his will to the Emperor and agreed to obey.