Amon - Council of Nikaea: The XV Legion was eventually able to rebuild its numbers (though the Thousand Sons Legion would never become as large as its fellow Legions) and return to the Great Crusade, led by their Primarch Magnus. Using their psychic gifts, the resurgent Thousand Sons Legion brought a number of worlds into Imperial Compliance, bringing them into the welcoming fold of the Imperial Truth.Their primary methods of victory included the use of diplomatic guile and trickery, a modus operandi that was not questioned by the rest of the Imperium. But these methods grew less effective as the XV Legion's expeditionary fleet entered more dangerous regions of unknown space where extensive hostile forces were encountered.Many of these new enemies of Mankind employed psychic powers similar to those that the Thousand Sons wielded. The XV Legion used their own potent psychic gifts and sorcerous abilities to bring these enemies of Mankind into Compliance or to exterminate them altogether.Over the following decades some of the primarchs voiced their dissent that these so-called "psyker" Astartes were allowed to exist and be a part of the Emperor's righteous Great Crusade. Rumours and condemnations began to spread about the Thousand Sons Legion amongst the other expeditionary fleets. The most vocal of these detractors were the primarchs of the Death Guard, Imperial Fists and Raven Guard Legions -- Mortarion, Rogal Dorn and Corvus Corax, respectively.The majority of the Astartes of the XV Legion had been afflicted by the rampant genetic mutation within their ranks. Those that still remained unafflicted had seen their psychic abilities increase dramatically in power level. Soon the Thousand Sons' detractors raised their objections to the Emperor Himself, calling for the XV Legion's disbandment and for the Legion to be expunged from the Imperial records like the II and XI Legions.The Emperor was also displeased by the Thousand Sons' dabblings in manipulating the corrupting powers of the Warp and later forbid the use of sorcery by either Magnus the Red or the members of his Legion after an Imperial Conclave was called on the world of Nikaea to deal with the question of psykers.While fighting in the Great Crusade, the Thousand Sons would secretly gather the sacred texts and forbidden research into psychic phenomena of several thousand conquered worlds and compile them into the infamous tome of sorcery known as the Book of Magnus.However, serious suspicion began to surround Magnus as the hatred towards mutants and psykers spread through the Imperium as the crusade progressed and the Legions learned how dangerous the use of psychic abilities could be on world after world that had been ravaged by them during the Age of Strife.After much debate in the Imperium over the use of psykers, the Emperor called an Imperial conclave of all the primarchs and chief Imperial officials at the remote and volatile planet of Nikaea to deal with the issue once and for all. The highest authorities in the young Imperium were present or were represented, including the Emperor and his Sigillite and Regent Malcador, who officiated over the council.At the forefront of the debate was Magnus, who argued very passionately for his cause and the important contributions that psykers and the use of sorcery could make to the improvement of the Imperium and to speeding up the successful conclusion of the Great Crusade.The main opponents to the use of psykers were the Space Wolves who shared their Primarch Leman Russ' hatred of sorcery as unclean and cowardly and the Death Guard, whose Primarch Mortarion testified in person against the use of psychic powers as he had known them to be abused on his own homeworld of Barbarus.When a consensus emerged among the council's participants that psykers and their powers represented a potential danger to the people of the Imperium, the Emperor's edicts were that in the interest of unity, no one was to be censured for prior actions involving the use of psychic abilities.However, the future use of psychic abilities by the Imperium's military forces was banned (except the use of Astropaths, Navigators, and very strictly sanctioned and controlled psykers who were authorised to carry out Imperial business, like the Sisters of Silence).All Astartes Legion Librarians were to be disbanded, and their members returned to conventional combat duty. In effect, Magnus and the Thousand Sons were banned from practicing "sorcery" or using the psychic abilities and knowledge they so coveted.During the council an unknown Warp entity took the guise of Amon in order to further the plans of the Chaos Gods to place the Thousand Sons and the Space Wolves at each others' throats. This entity, in a complicated, multi-tiered and long-planned scheme driven by Tzeentch, presented a version of events to Kasper Ansbach Hawser that implicated Hawser as a Hidden One of the Thousand Sons, planted and controlled by Amon in a spying operation designed to give the Thousand Sons intelligence on the Space Wolves.When confronted by Bjorn of the Space Wolves and Amon Tauromachian of the Legio Custodes, the simulacrum of Amon responded with violence before escaping.This event only reinforced the belief amongst several senior Imperial figures that the Thousand Sons were out of control and was immediately told to the Emperor.The event may have had bearing upon the eventual decision of the Emperor concerning the fate of the Thousand Sons and the ban placed on Librarians in general by the Edicts of Nikaea. The real Amon was later said to have been at Magnus' side thoughout the Council, unaware of the actiosn taken by his doppelganger.