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"If I am guilty of anything it is the simple pursuit of knowledge."

Magnus the Red during the Council of Nikaea
Magnus the Red Primarchs coverart

Magnus the Red, the Crimson King, Primarch of the Thousand Sons Legion during the Great Crusade. Magnus was the primary proponent of the use of Warp powers during the Council of Nikaea.

The Council of Nikaea was a great Imperial conclave called by the Emperor of Mankind in 001.M31 on the world of Nikaea in the midst of the Great Crusade that was intended to determine whether or not the use of psychic powers represented a boon or a grave danger to Humanity and the newborn Imperium of Man.

Ultimately, in the Decree Absolute of the Emperor that emerged from the council, the existence of certain psykers like Navigators and astropaths in the Imperium was sanctioned but tightly restricted under centralised Imperial control. The potent and unrestricted use of psychic abilities that was defined as "sorcery" -- bargaining for power or knowledge with the intelligent entities that existed within the Warp -- was officially banned.

Additionally, the existence of the department of the Librarius found in most Space Marine Legions of the era was banned, and the Librarians themselves, who served as the Legion's combat psykers, were ordered to return to the duties of simple battleline Astartes and never to use their abilities again.

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 and the Fall of Prospero.

The ban on Librarians and other sanctioned combat psykers was later relaxed during the campaigns of the Great Scouring largely due to the events of the Horus Heresy and the realisation that the forces of Chaos could not be defeated by Imperial forces without at least tightly controlled access to the power of the Immaterium.

It was also at the Council of Nikaea that the "Chaplain Edict" was promulgated by the Emperor, requiring every Space Marine Legion to establish a new specialty rank whose holder was known as a "Chaplain," based on the practice of the Word Bearers Legion.

A Chaplain was charged with ensuring that every Legion remained committed to the ideals of the Imperial Truth and to help maintain the dedication, morale and faithfulness of its battle-brothers to the vision of the Emperor.

Within the archives of the Blood Ravens, the Council of Nikaea is known as the "Hearing of the Thousands." Furthermore, the Apocrypha of Haidyes -- "Knowledge is power; use it well" -- was used during the council which later became the Chapter motto of the Blood Ravens.

The Debate

"Many have spoken of the evils of the psyker, the sorcerer and the witch; that the art is intrinsically wrong simply because it can be used to perform terrible deeds. I say that one must instead consider that this evil is a projection of the fears of the many who do not understand the possibilities that await Mankind if we can tame the dangers of this art. That it is this multitude of lesser sins that is the real issue for this Council."

—Magnus the Red, as recorded during the Council of Nikaea, 001.M31

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 spiritually 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 were 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 xenos 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.

These "Librarians" -- so named because they soon became the keepers of their Legion's storehouses of knowledge and history -- 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. Corvus 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 levelled 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 extensive 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 individuals 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, 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.

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 of Nikaea 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 offence against Mankind and the worst kind of heresy against the Imperial Truth.

Yet 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 many Terran 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 and the existence of the terrible entities later known by Humanity as the Chaos Gods to which only they remained privy, but now it appeared that His gene-son had disobeyed His edicts and at the very least dabbled in the occult and the forbidden black arts of sorcery by repeatedly treating with the denizens of the Warp. The confrontation between father and son is recorded in the Grimoire Hereticus.

As a result, 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' proposed compromise between the practice of restrained combat psyker abilities and the pursuit of true sorcery. 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 Emperor decreed that the Space Marine Legions were no longer to employ combat psykers within their ranks.

He commanded that the primarchs were to close the Librarius departments of their Legions 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 of Nikaea's rulings also created a new position amongst the Space Marine Legions, the Space Marine Chaplain, drawn from the practices of the Word Bearers Legion, 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 immediately, 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 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 and of combat pyskers in the wider Imperial military forces would be reversed as a result of the Horus Heresy, as that terrible civil war made clear to the rulers of the Imperium that combat psykers were essential to face the fell powers of the forces of Chaos. In this way, the Librarians' original compromise that the Emperor rejected at Nikaea eventually became the Imperium's de facto policy concerning psykers in the wake of the Horus Heresy.

In the 41st Millennium, the choice of whether to make use of Librarians was left to each Chapter of the Adeptus Astartes to decide for itself. For instance, the Salamanders explained to their rivals the Marines Malevolent that they felt the strictures of Nikea were outdated and psychic powers should be cultivated more assiduously, while the Marines Malevolent and many other Chapters retained a healthy distrust of psykers and all those who dealt with the Immaterium.

The Emperor's Decree Absolute

Below is a transcript of the Emperor's speech upon making His Decree Absolute that became known as 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."

Notable Attendees and Stance on Use of Psykers

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 the 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 Members

Stance on Psykers
Emperor of Mankind The guardian of Humanity and supreme ruler of the Imperium of Mankind. Even in the years following the Horus Heresy, it is frowned upon to speculate at the Emperor's hidden plans, and it is impossible to accurately guess His true intentions for the conclave.
Malcador the Sigillite High Proconsul Imperialis and Regent of Terra, who served as the Emperor's most trusted advisor. Malcador was the chief counselor to the Emperor and acted as the Convener of the Council of Nikaea. His stance on the psyker issue is unknown.
Kelbor-Hal Fabricator-General of Mars* Vehemently against the use of psykers.
Tabor Ludovicia Lord Militant, Muster of the Imperialis Auxilia Openly favoured either side.
Haldane Ma'lon Lord Militant, Muster of the Imperialis Auxilia Openly favoured either side.
Constansa Suati-Falkan Grand Admiral, Imperialis Armada Vehemently against the use of psykers.
Jalisco de Jerichos Huerta Occulex-Magister, Ordo Astra Telepathica Avowed neutrality on the issue.
Constantin Valdor Captain-General, Chief Custodian of the Legio Custodes Favoured neither side.

Legiones Astartes Primarchs

Stance on Psykers
Lion El'Jonson Lord of the I Legion Openly favoured neither side, but known to favour the censure of Magnus.
Fulgrim Lord of the III Legion* Proponent of continued psyker use, despite the fact that his own Legion made little or no use of psykers.
Perturabo Lord of the IV Legion* Opposed the use of psykers.
Jaghatai Khan Lord of the V Legion Supported continued use of psykers.
Leman Russ Lord of the VI Legion Vehemently against use of psykers.
Rogal Dorn Lord of the VII Legion Known not to favour use of psykers.
Konrad Curze Lord of the VIII Legion* Supported use of psykers.
Sanguinius Lord of the IX Legion Proponent of the use of psykers.
Ferrus Manus Lord of the X Legion Did not favour the use of psykers.
Angron Lord of the XII Legion* Vehemently against the use of psykers.
Roboute Guilliman Lord of the XIII Legion Less vocal proponent of psyker use.
Mortarion Lord of the XIV Legion* Vehemently against use of psykers.
Magnus the Red Lord of the XV Legion* Adamantly in favour of psyker use.
Horus Lupercal Lord of the XVI Legion, Warmaster of the Imperium* Openly favoured neither side.
Lorgar Aurelian Lord of the XVII Legion* Supported the use of psykers.
Vulkan Lord of the XVIII Legion Supported the use of psykers.
Corvus Corax Lord of the XIX Legion Favoured the censure of Magnus.
Alpharius Lord of the XX Legion* Supported the use of psykers.
  • These leaders later threw their support behind Horus during the dark years of the Horus Heresy.

Other Notable Personnel

Stance on Psykers
Elikas Chief Librarian of the I Legion Supported the use of psykers.
Eidolon Lord Commander of the III Legion* Unknown, but more than likely favoured whatever position his Primarch held.
Vespasian Lord Commander of the III Legion Unknown, but more than likely favoured whatever position his Primarch held.
Targutai Yesugei Stormseer of the V Legion Supported the use of psykers. He presented the Council of Nikaea a third option in regards to the use of psychic abilities. 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.
Aun Helwintr Priest of Fenris of the VI Legion Vehemently against the use of psykers.
Ohthere Wyrdmake Priest of Fenris of the VI Legion Vehemently against the use of psykers. Wyrdmake initially befriended Chief Librarian 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.
Fel Zharost Chief Librarian of the VIII Legion Adamantly in favour of psyker use.
Raldoron Chapter Master and First Captain of the IX Legion Proponent of psyker use, but made clear that he would respect whatever ruling the Emperor made.
Ahzek Ahriman Chief Librarian and Captain of the 1st Fellowship of the XV Legion* Adamantly in favour of psyker use, like his Primarch.
Magistus Amon Equerry to Magnus the Red and Captain of the 9th Fellowship of the XV Legion* Adamantly in favour of psyker use.
Promos Chief Librarian of the XIII Legion Supported psyker use.
Calas Typhon First Captain of the 1st Company of the XIV Legion* Unknown, but more than likely favoured whatever position his Primarch held.
Umojen Chief Librarian of the XVIII Legion Supported psyker use.
  • These personnel later threw their support behind Horus during the dark years of the Horus Heresy.



Warhammer 40,000 Grim Dark Lore Part 19 – Council of Nikaea


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.


  • Blood Ravens: The Dawn of War Omnibus (Novel) by C.S. Goto, "The Trials of Isador," pp. 270-272
  • 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
  • The Horus Heresy - Book Three: Ecterminmation (Forge World Series) by Alan Bligh, pg. 19
  • The Horus Heresy - Book Seven: Inferno (Forge World Series) by Alan Bligh, pp. 14, 55
  • A Thousand Sons (Novel) by Graham McNeill
  • Prospero Burns (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, Part I, pg. 91
  • Blood Ravens: The Dawn of War Omnibus, "The Trials of Isador" (Short Story) by C.S. Goto, pp. 270-272
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Warhammer 40,000 Overview Grim Dark Lore Teaser TrailerPart 1: ExodusPart 2: The Golden AgePart 3: Old NightPart 4: Rise of the EmperorPart 5: UnityPart 6: Lords of MarsPart 7: The Machine GodPart 8: ImperiumPart 9: The Fall of the AeldariPart 10: Gods and DaemonsPart 11: Great Crusade BeginsPart 12: The Son of StrifePart 13: Lost and FoundPart 14: A Thousand SonsPart 15: Bearer of the WordPart 16: The Perfect CityPart 17: Triumph at UllanorPart 18: Return to TerraPart 19: Council of NikaeaPart 20: Serpent in the GardenPart 21: Horus FallingPart 22: TraitorsPart 23: Folly of MagnusPart 24: Dark GambitsPart 25: HeresyPart 26: Flight of the EisensteinPart 27: MassacrePart 28: Requiem for a DreamPart 29: The SiegePart 30: Imperium InvictusPart 31: The Age of RebirthPart 32: The Rise of AbaddonPart 33: Saints and BeastsPart 34: InterregnumPart 35: Age of ApostasyPart 36: The Great DevourerPart 37: The Time of EndingPart 38: The 13th Black CrusadePart 39: ResurrectionPart 40: Indomitus