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Council of Nikaea

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Magnus The Red Portrait

Portrait of Magnus the Red, the Crimson King, Primarch of the Thousand Sons Legion

The Council of Nikaea was a great Imperial conclave called by the Emperor of Mankind during the early 31st Millennium on the world of Nikaea in the midst of the Great Crusade that was intended to determine whether or not the use of psychic sorcery represented a boon or a grave danger to Mankind and the newborn Imperium of Man. Ultimately the existence of psykers in the Imperium was allowed but tightly restricted under centralised Imperial control, 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, ultimately leading to their damnation by Chaos during the early days of the Horus Heresy.

The Debate

"If I am guilty of anything it is the simple pursuit of knowledge."
Magnus the Red during the Council of Nikaea

There was an increasing concern as the Great Crusade progressed about the use of psychic abilities. The Emperor was of course the most powerful human psyker to have ever lived, but he was deeply ambivalent about the spread of the mutant psyker genes through more and more of the human population, as he rightly believed that most of Mankind was not yet evolved enough either physically or spirituallty to truly control the great power of the Warp or avoid the temptations offered by its more malevolent denizens. More and more often during the progress of the Imperial conquest of the galaxy, the Imperial Army and Space Marines would make planetfall only to find that the populace was in thrall to mysterious powers and unnatural mystics and so-called "sorcerers." These people were essentially members of Chaos Cults who would resist the forces of the Emperor with sorcerous powers granted them by daemonic entities from the Warp.

These powers were also very akin to those used by the Thousand Sons Legion of the Primarch Magnus the Red. The Thousand Sons had come under criticism for their use of sorcery by the Primarch Mortarion of the Death Guard Legion, who knew by his own personal experience with sorcerers on his homeworld of Barbarus the dangers to be found in anything spawned from the Warp, and Leman Russ of the Space Wolves Legion, for whom any battle fought through sleight of hand, clever deceit or any trick other than straight physical combat was by definition dishonourable. Russ found the Thousand Sons' use of sorcery distasteful in the extreme and it was Russ who had fought the hardest for the Imperium to ban the use of psychic powers after his own experiences during several campaigns of the Great Crusade where his Space Wolves had fought beside the Thousand Sons. The schism grew so great that it threatened the very stability of the fledgling Imperium and so the Emperor himself had called for an Imperial conclave to resolve the issue once and for all.

Unlike his brother Primarchs, Magnus the Red saw the potential in exploiting the powers of psychically talented Astartes and he had been instrumental in the development of the Space Marines' corps of Librarians. In some of the Astartes Legions the psychic mutation was relatively common and it was felt by some of the Primarchs that such individuals should be allowed to continue to use their innate psychic abilities for the benefit of the Legion. This would allow these gifted Battle-Brothers to be of use to their Legion without presenting any danger to their fellows or to the civilians of the Imperium. Magnus and a number of other Primarchs created a program for the training and development of psyker Astartes that supplemented the traditional process for creating a new Space Marine. The Emperor was asked to approve of the recruitment of these psykers into the ranks of those Legions who wished to make use of them, and he sanctioned these first experiments as a means of controlling the spontaneous outbreaks of psychic mutation within the ranks of the Legions. The Librarians quickly proved to be loyal and effective warriors and soon gained acceptance by the Emperor and the Primarchs for their presence on the battlefield. The Librarians became a powerful addition to the ranks of the Space Marine Legions.

However, there were those Primarchs who raised their voices in dissent, arguing amongst themselves and with the Emperor that Librarians should not be permitted within the ranks of the Astartes. Some desired to expand their Legions' Librarius and recruit even more Librarians into their ranks, whilst other Primarchs vehemently opposed the entire notion of Librarians and felt that they should be expunged from their ranks altogether. Primarchs such as Leman Russ felt that Librarians were no better than witches. Corax and Rogal Dorn also refused to commit their Legions to fight alongside other Legions that made use of Librarians. Mortarion in particular accused his brother Magnus of using the forbidden arts of sorcery.

Dismayed at the accusations leveled against Magnus and the friction the issue was causing amongst his Primarchs, the Emperor was also concerned about the Librarians and the dangers they presented to the Great Crusade when he was no longer fighting directly alongside his Space Marine Legions. Before departing for Terra to begin his secret Imperial Webway Project within the seclusion of the Imperial Palace's dungeons, he summoned the Primarchs and all the other major Imperial leaders to a War Council summit on the world of Nikaea to address the Librarian crisis.

Both sides of the debate over the use of psychic abilities arrived at the world of Nikaea determined to present their views, with the Emperor as the arbiter, enthroned above the dais in an ancient amphitheater that seated tens of thousands where the conclave was held. On one side of the question were the Witch Hunters like the Sisters of Silence who presented their case by reciting a litany of the human suffering inflicted upon the Emperor's own subjects by sorcerers enslaved by what would later be recognised during the Horus Heresy as Chaos, of gibbering mutants who had lost their humanity, and of cults and power-hungry men who turned their psychic gifts to dark purposes. All present were also aware of the terrible damage that had been done by uncontrolled and daemon-possessed psykers during the early days of the Age of Strife. On the other side was a powerful advocate for the continued use of sorcery, the Primarch Magnus the Red. His very presence frightened many, but he began to speak with the great charisma that only a Primarch could wield. His argument was that no knowledge was tainted in and of itself, and no pursuit of knowledge was ever wrong so long as the seeker of that truth was the master of what he learned rather than its pawn. He spoke with finality that his Thousand Sons Astartes had mastered their knowledge of sorcery and that there was no knowledge too labyrinthine for them to grasp or that they could not master to serve Mankind rather than enslaving it. Magnus called on the Emperor not to ban the use of psychic abilities, but to contribute to further research into their usage so that they might be harnessed more fully for the betterment of humanity and the Imperium.

The Edicts of Nikaea

"If you treat with the Warp, Magnus, I shall visit destruction upon you. And your Legion's name will be struck from the Imperial records for all time."
— The Emperor of Mankind, part of his Decree Absolute during the Council of Nikaea

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 present 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 Librarian Epistolary who spoke for the group. A psyker, he proposed, was like an athlete, a gifted individual whose native talent must be carefully nurtured. Psykers were not innately evil in themselves, but like any tool, could be used for either good or evil purposes. 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 truly sure who or what had 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.

The Council of Nikaea was also the trial of Magnus the Red -- for he was accused of sorcery and of introducing sorcerous practices to the Space Marine Legions through the institution of the corps of Librarians. As the evidence of Magnus' continued practice of sorcery became apparent, the Emperor barely contained his wrath as he pronounced judgement on the Primarch of the Thousand Sons, for he had entrusted his son years before to obey his bidding and foreswear the use of such occult practices because of the dangers inherent to the Warp. He had entrusted only Magnus with the true secrets of the Warp to which only they remained privy, but now it appeared that his son had disobeyed his edicts and at the very least dabbled in the occult and the forbidden black arts of psychic sorcery. The confrontation between father and son is recorded in the Grimoire Hereticus.

The Emperor's judgement at the Council of Nikaea proved severe, largely as a result of his anger at Magnus. The Emperor rejected the Librarians' compromise. With the exceptions of Navigators and Astropaths who were properly trained, controlled and sanctioned by the Imperium and were necessary to its continued existence, the Space Marine Legions were no longer to employ psykers within their ranks. He commanded that the Primarchs were to close their Librarius departments forthwith and not to indulge the undoubted psychic talents of those Astartes who possessed the gift. All existing Space Marine Librarians were likewise forbidden to make use of their abilities. The Council's rulings also created a new position amongst the Space Marine Legions, the Space Marine Chaplain, to uphold the Imperial Truth and help maintain the purity of an Astartes Legion's dedication and fidelity to the Emperor's commands.

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 he remained bitterly opposed to the decision made at Nikaea. But in the end, he bent his will to his father the Emperor and agreed to obey, though the machinations of the Ruinous Powers would ultimately lead to a far darker fate for Magnus the Red and his Thousand Sons. The Edicts of Nikaea stood largely untouched for the next 10,000 standard years as the primary Imperial policy regarding human psychic mutation. Only the edict against the use of Librarians within the ranks of the Space Marines would be reversed as a result of the Horus Heresy, as that terrible civil war made clear to the rulers of the Imperium that Astartes psykers were essential to combat the power of the Forces of Chaos.

Notable Attendees

The following is a list of the notable attendees of the Council of Nikaea. There were also several individuals in attendance who sat in reserved cantilevered boxes. Instead of defining forms, a person only saw shadows and reflections, each box filled with bent creases of light. These were known as "falsehoods." Though there were unmistakably real people within each box, Imperial technological artifice concealed them from the sight of the rest of the Council. Whoever occupied the boxes retained their anonymity by virtue of chameleonic cloaks that shielded them from the casual sight of observers. The Emperor ordered that such falsehoods should be used so that no individual's testimony would be corrupted by the fear of those whose eyes were upon them. It was later implied by the Thousand Sons Legion's Chief Librarian Ahzek Ahriman that several of the individuals behind these falsehoods were Primarchs from other Space Marine Legions.

Council of Terra

  • Emperor of Mankind
  • Malcador the Sigillite - The Emperor's most trusted advisor, Malcador was the chief counselor to the Emperor and acted as the Convener of the Council of Nikaea.
  • Kelbor-Hal - Kelbor-Hal was the Fabricator-General of the Adeptus Mechanicus, and sat on the Council of Nikaea. His position in regards to the continued use of psychic abilities and the existence of the Space Marine Legions' Libraria is unknown.
  • Choirmaster of Astropaths
  • Master of Navigators
  • Lord Militant of the Imperial Army

Space Marines

  • Magnus the Red - Primarch of the Thousand Sons Legion. He stood firmly in favour of the continued use of psychic abilities and the established Legion Libraria.
  • Fulgrim - Primarch of the Emperor's Children Legion. He stood firmly behind his brother Magnus in support of the continued use of psychic abilities and the established Legion Libraria, despite the fact that his own Legion made little or no use of psykers.
  • Sanguinius - Primarch of the Blood Angels Legion. Sanguinius supported his brothers Magnus and Fulgrim position for the continued use of psychic abilities and the maintenance of the established Legion Libraria.
  • Leman Russ - Primarch of the Space Wolves Legion. Russ was firmly opposed to the continued use of psychic abilities within the Imperium and anything that wreaked of sorcery, and believed that the Legions' Libraria should be disbanded.
  • Mortarion - Primarch of the Death Guard Legion. Like Russ, Mortarion was firmly opposed to the use of psychic powers because of his past experiences on his homeworld of Barbarus and also believed that the Legions' Libraria should be disbanded.
  • Ahzek Ahriman - Chief Librarian and Captain of the Thousand Sons Legion's 1st Fellowship. He firmly supported his Primarch Magnus in pushing for the continued use of psychic abilities as well as the maintenance of the Legions' corps of Librarians.
  • Amon - Captain of the 9th Fellowship and Equerry to Magnus the Red.
  • Raldoron - Raldoron was the First Captain of the Blood Angels Legion. Chapter Master Raldoron firmly stood behind his Primarch's position in regards to the continued use of psychic abilities and the maintenance of the established Legion Libraria, but made clear that he would respect whatever ruling the Emperor made in regards to these matters.
  • Calas Typhon - First Captain of the Death Guard Legion. It is unknown what his personal position was in regards to the continued use of psychic abilities within the Legiones Astartes, but one could assume that he firmly stood behind his Primarch's position in this matter.
  • Eidolon - Lord Commander of the Emperor's Children. His position in regards to the continued use of psychic abilities and the Legions' Libraria is unknown. But one could assume that he firmly supported whatever position his Primarch held.
  • Vespasian - Lord Commander of the Emperor's Children. His position in regards to the continued use of psychic abilities and the Legions' Libraria is unknown. But one could assume that he firmly supported whatever position his Primarch held.
  • Elikas - Elikas was the Chief Librarian of the Dark Angels Legion. He firmly stood for the continued use of psychic abilities within the Legiones Astartes as well as the maintenance of the Legions' established Libraria.
  • Aun Helwintr - A Rune Priest of the Space Wolves Legion. He was vehemently against the continued use of psychic abilites within the Legiones Astartes and also favoured the disbandment of the Legions' Libraria.
  • Promus - Chief Librarian of the Ultramarines Legion. He firmly stood for the continued use of psychic abilities within the Legiones Astartes as well as their maintenance of their established Libraria.
  • Umojen - Umojen was the Chief Librarian of the Salamanders Legion. He firmly supported the continued use of psychic abilities within the Legiones Astartes as well as the maintenance of their established Libraria.
  • Ohthere Wyrdmake - Ohthere Wyrdmake was a Rune Priest of the Space Wolves Legion. Wyrdmake befriended Ahzek Ahriman of the Thousand Sons in an attempt to learn more about the sorcerous tenets of his Legion. When the time came, he betrayed Ahriman's trust and spoke out against the Thousand Sons' continued use of sorcery and their predilection for delving into forbidden knowledge during the Council of Nikea.
  • Targutai Yesugei - Yesugei was a junior Stormseer of the White Scars Legion. He presented the Council of Nikaea a third option in regards to the use of psychic abilities and the maintenance or abolition of the established Legions' Libraria. He explained that there was nothing inherently evil about a Librarian. If such a gifted individual was properly trained in order to obtain the greatest results, like any weapon, he or she could be still be used, but with respect and not indiscriminately. Yesugei argued that human psykers should be trained rigorously to take advantage of their innate abilities in order to assist the Imperium in completing its galaxy-wide spanning conquest. With such an elite cadre of trained psychic specialists utterly loyal to the Emperor, the galaxy could be brought back into the Imperial fold with ease. Yesugei also argued that psychic sorcery should be strictly forbidden, since in dealing with the entities of the Warp, the ever-present risk of corruption was simply too great to be avoided. This position would later be vindicated in the wake of the Horus Heresy and would become the default policy of the Imperium towards psykers during the Age of the Imperium.
  • Zharost - Zharost was the Chief Librarian of the Night Lords Legion. He firmly supported the continued use of psychic abilities within the Legiones Astartes as well as the maintenance of the Legions' established Libraria.

The Emperor's Ruling

Below is a transcript of the Emperor's speech upon decreeing the Edicts of Nikaea, drawn from the oldest of Imperial records:

"Hear now the words of my ruling.
I am not blind to the needs of the Imperium, but nor am I blind to the realities of the hearts of men. I hear men speak of knowledge and power as though they are abstract concepts to be employed as simply as a sword or gun. They are not. Power is a living force, and the danger with power is obsession. A man who attains a measure of power will find it comes to dominate his life until all he can think of is the acquisition of more. Nearly all men can stand adversity, but few can stand the ultimate test of character, that of wielding power without succumbing to its darker temptations.
Peering into the darkness to gain knowledge of the Warp is fraught with peril, for it is an inconstant place of shifting reality, capricious lies and untruths. The seeker after truth must have a care he is not deceived, for false knowledge is far more dangerous than ignorance. All men wish to possess knowledge, but few are willing to pay the price. Always men will seek to take the short cut, the quick route to power, and it is a man’s own mind, not his enemy or foe, that will lure him to evil ways. True knowledge is gained only after the acquisition of wisdom. Without wisdom, a powerful person does not become more powerful, he becomes reckless. His power will turn on him and eventually destroy all he has built.
I have walked paths no man can know and faced the unnameable creatures of the Warp. I understand all too well the secrets and dangers that lurk in its hidden darkness. Such things are not for lesser minds to know; no matter how powerful or knowledgeable they believe themselves to be. The secrets I have shared serve as warnings, not enticements to explore further. Only death and damnation await those who pry too deeply into secrets not meant for mortals.
I see now I have allowed my sons to delve too profoundly into matters I should never have permitted them to know even existed. Let it be known that no one shall suffer censure, for this conclave is to serve Unity, not discord. But no more shall the threat of sorcery be allowed to taint the warriors of the Astartes. Henceforth, it is my will that no Legion will maintain a Librarius department. All its warriors and instructors must be returned to the battle companies and never again employ any psychic powers.
Woe betide he who ignores my warning or breaks faith with me. He shall be my enemy, and I will visit such destruction upon him and all his followers that, until the end of all things, he shall rue the day he turned from my light."


The term "Council of Nikaea" is a historical reference to the Christian Church's Council of Nicaea, which occurred in the year 325 AD in the Roman Empire's province of Asia (Asia Minor) and was hosted by the Emperor Constantine the Great. This Council of Nicaea determined the content of orthodox Christian belief as laid out in the Nicene Creed of the Roman Catholic, Protestant and Eastern Orthodox Churches.


  • Horus Heresy: Collected Visions, pp. 92-94
  • Index Astartes I, "Psykana Librarius - Space Marine Librarians"
  • Index Astartes III, "Masters of Forbidden Knowledge - The Thousand Sons Space Marine Legion"
  • The Horus Heresy - Visions of Heresy: Book One (Art Book) by Alan Merrett, pp. 146, 148
  • A Thousand Sons (Novel) by Graham McNeill
  • Prospero Burn (Novel) by Dan Abnett
  • Know No Fear (Novel) by Dan Abnett
  • Fear to Tread (Novel) by James Swallow
  • Garro: Legion of One (Audio Book) by James Swallow
  • Salamander (Novel) by Nick Kyme
  • Blood Ravens: The Dawn of War Omnibus, "The Trials of Isador" (Short Story) by C.S. Goto, pp. 270-272

Start a Discussion Discussions about Council of Nikaea

  • Did the Luna Wolves utilize Librarians?

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    • One of Abaddon's Chosen is the Lord Deceiver Ygethmor, a powerful Chaos Sorcerer and it is hinted that he may have been a Librarian of the Sons...

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