Librarian Consul - Council of Nikaea: As the 31st Millennium dawned, there were those within the Great Crusade who believed that the Thousand Sons Legion and their master had simply gone too far down a road long prohibited by the Emperor: the path of "sorcery." But what is sorcery? To many, particularly those of superstitious mind, the manifestation of any psychic power might be called such, and there is perhaps some truth to this belief as all psychic abilities, no matter how rigidly controlled or slight in effect, are perilous by their very nature.But the more common definition has always held that the term sorcery was more readily applied in the Age of the Imperium to the reckless pursuit of psychic power without due measures of control or caution, particularly the use of certain forbidden texts and practices of ancient Human and xenos origin and any practice that required bargaining for knowledge and power with the malevolent entities of the Warp.These arts, pursued in order to master forces of terrible power and breadth without any of the sanction or stricture the Emperor had enforced on His new Human civilisation, were to any sane mind understood to be incredibly dangerous, not only to the individual who sought them out, but to all around them. In short, they were the sins of the past wilfully repeated, and it was of this that the Thousand Sons were generally suspected.The loudest voices that called for the censure of the Thousand Sons Legion for straying from the path of sanity and law were those of Primarchs Leman Russ of the Space Wolves, Corvus Corax of the Raven Guard and Mortarion of the Death Guard. All three had at various times come face-to-face with the all but unimaginable horrors that could result from the ultimate misuse of psychic power and feared that if left to their own devices, the Thousand Sons would bring such a calamity upon themselves and the worlds of the fledgling Imperium.This opinion had behind it the weight of history, for the Old Night that had consumed the interstellar Human civilisation of the Age of Technology and brought about the long Age of Strife was often considered to have had its origins in the proliferation of powerful and unrestrained psykers. To their detractors, such as Russ and Mortarion, psykers in the ranks of the Legiones Astartes were fundamentally suspect. This was because they often had none of the overt limitations imposed upon the psykers of the Scholastica Psykana and little direct oversight as was found elsewhere in the Imperium.This was doubly the case with the Thousand Sons, a Space Marine Legion who by its gene-seed's influence at its core formed one of the greatest concentrations of psykers ever encountered, and as time progressed, suspicion grew of the outsider XVth Legion, its hidden ways and its arcane secrets.Eventually, to address these growing concerns, in 001.M31 the Emperor called a great Imperial conclave, the Council of Nikaea, on the newly-terraformed planet of the same name, to determine whether Human psychic powers and the practice of psychic sorcery presented a danger to the newborn Imperium and its people. Ultimately, following the testimonials of the council, the Emperor refused any compromise and ordered all of the Space Marine Legions to disband their Librarius Corps and for all of the Librarians of the Legions to return to service as line warriors and never use their psychic abilities again.