Council of Nikaea
The Council of Nikaea was a great convocation called by the Emperor of Mankind to discuss the use of psychic powers in the Imperium, particularly within the Legiones Astartes. It took place in the waning years of the Great Crusade, and would be one of the last notable gatherings of historically important personages before the outbreak of the Horus Heresy. While termed a 'council', the methodology of the debate and the persecution they felt they suffered because of it led the Thousand Sons Space Marine Legion to refer to the event as the Trial of the Thousand Sons or the Trial of Magnus the Red.[Needs Citation] To some later Imperial scholars, the Council was also known as the Hearing of the Thousands.
The Librarian Crisis
The young Imperium was wary of the development of psychic potential among the population; the means to reasonably successfully monitor and control such mutant developments did not yet exist, and there was deep distrust and bias amongst the various factions that saw, or did not see, a benefit to allowing those with psychic powers to remain unchained...or even alive. Many individuals with psychic powers were put to use by the Imperium, the most important being the Navigators who made safe space-travel possible, but even these psykers were barely tolerated by some. Any grouping of psykers was bound to draw comment, and so it proved with the Thousand Sons Legiones Astartes.
The Thousand Sons drew regular criticism simply for existing throughout much of the early part of their career, seen as potentially dangerous due to the psychic talents of their Legionaries. Anti-psykers decried them as an example of the problem writ large, an imminent threat to the Imperium. Cries for their disbandment were loud; the discovery of their primarch, Magnus, quietened these calls for a time.
Magnus and two other primarchs - Sanguinius of the Blood Angels, and Jaghatai Khan of the White Scars - proposed that Librarius Departments should be formed in the Legions to harness the latent psychic powers that were beginning to manifest in the Astartes of some Legions. Initially, the Emperor sanctioned the experiments and then allowed the deliberate recruitment of psychic candidates into Legions that did not already posses such mutants; however, as he withdrew from the fighting of the crusade, many called for him to pass judgment on whether the experiment should continue.[2d] 
The reasoning for this was twofold. Firstly, as the Great Crusade reached further from the light of Terra, stranger and stranger foes were faced. Many times the Legiones Astartes or the Imperial Army would discover a new world, only to be met by hostile action from beings who wielded mysterious, sorcerous-seeming powers; powers that resembled those employed by the Thousand Sons and the legion Librarians.
The second was that the Thousand Sons were seen to be potentially dangerously unstable by none other than Leman Russ, primarch of the Space Wolves and long a distruster of the Thousand Sons' martial doctrines and battle-philosophy. On the world of Shrike, the Russ witnessed a Thousand Son fall victim to a malady called the flesh-change; uncontrolled physical degeneration and grand mal mutation apparently brought on by the loss of psychic control. Announcing that he had turned a blind eye to Magnus' "obvious" dabbling in black arts up to this point, the Wolf King declared that he was done ignoring his brother's tainted ways and claimed that the entire Thousand Sons legion was corrupted. He further promised a reckoning.[2a]
Leman Russ' voice joined that of Mortarion's, long a critic of the Thousand Sons and psykers in general and who now openly accused Magnus of sorcery, and that of Corax and Rogal Dorn, who both refused to field their Legions alongside the Thousand Sons and even other legions that deployed Librarians upon occasion. Their outcry now so insistent that it soon became a major point of contention across the entire Imperium, with the primarchs split over the issue. Eventually, on the brink of leaving the Great Crusade after the ascension of Horus Lupercal to the position of Warmaster, the Emperor was forced to call a conclave of the War Council of the Great Crusade to resolve the issue of psykers amidst the Legiones Astartes, with himself acting as arbiter. The world chosen for the great Council was called Nikaea.
Nikaea was a world that, during the time of the Great Crusade, was in its geological infancy. Clouds completely obscured the surface while tectonic movement created constant pyroclastic eruptions and storms across the planet. It's very fabric in flux, clods of ejected matter were caught in orbit or drifted across the system, with gravitational waves and electromagnetic discharges swamping local space. Navigating through all this to a point on the surface would've been impossible if not for a psychic beacon generated by the Emperor. The planet was said to be galactically remote. The surface of the still-forming world was littered with curious extrusions of rock and magma that had taken on various largely geometric shapes; Magnus claimed that this oddity was likely a reason the Emperor had selected the planet, as it echoed the origins of Magnus' belief in the ordered nature of the universe.[2b]
Perturabo both designed and built the council chambers. Although originally designed as an arena for competitive events, The Emperor would later repurpose it for his own use. The council chambers were created on Nikaea within a hollowed out stratovolcano, a massive amphitheatre having been carved out of it's heart. The beacon projected by the Emperor was visible to those with mindsight as a beam of light shooting straight up out of the volcano, wreathed in golden lighting. Magnus saw this as a magnificent sign of the wonders of psychic powers and a validation of his stance before the Council even began. His Chief Librarian Ahzek Ahriman, on the other hand, was dismayed by the sheer power on display, realising it was tied to a prophetic vision he had previously experienced that promised disaster. Casual use of psychic powers at the Council was difficult; Ahriman put this down to the presence of the Emperor.[2b]
Security within the Council was a privilege taken by the Adeptus Custodes, as was their right and duty when the Emperor himself was present; though a three-Company-strong force of Space Wolves were present to act - according to them - as a no-quarter safety measure in case Magnus made the 'wrong decision' in reaction to events. They were accompanied by a detachment of the Sisters of Silence, which made their presence (and that of their primarch, Leman Russ) psychically undetectable. Arrivals to the Council site had to submit control of their vessels to Custodes remote pilots, who berthed the ships at secured landing zones. Private quarters for attendees ringed the amphitheatre, which itself could seat thousands upon the tiered black stone seating. The amphitheatre was open to the elements, but workings of the Mechanicum kept the storm at bay. Massive environmental control machinery allowed the juvenile world to prematurely support life. The command and control position for the entire installation was staffed by several hundred operatives of the Imperial Fleet, the Hegemonic Corps, the Space Wolves, the Sisters of Silence and the Adeptus Custodes. The Emperor and his immediate retinue sat upon a pyramidal dias at one side of the amphitheatre (the side opposite on which Magnus' quarters were located).[2b]
The Council Convenes
The Council was presided over by Malcador the Sigillite, Regent Lord of Terra and personal confidant of the Emperor. He carried the Emperor's golden scepter as a sign that he held authority over the assembled. The Thousand Sons delegation was the last to arrive, uninformed of the true nature of the Council. Immediately after their arrival, Magnus and Ahriman were taken into the crowded public amphitheatre to be sworn in; it was at this moment that they realised, wearily and with shocked dismay respectively, the true nature of the 'council' they had been summoned to attend, at least for them.[2b]
The primary objective of the Council of Nikaea was to determine what to do about the Librarian Crisis that described the division between the Legions over the continued use of Librarians on the battlefield and for Magnus to face the charges of sorcery. Many interpreted the Council as in actuality the Trial of Magnus the Red; he was accused of sorcery and of corrupting the Space Marine Legions through the introduction of Librarians into them and their training by seconded warrior-scholars of the Thousand Sons.[2d]
Malcador announced that those gathered had been summoned to freely debate the issue - causing some consternation in the crowd - and whether the use of Librarians was outright sorcery that caused a threat to human galactic domination, or if such claims were fearful, ignorant mewlings. He closed this opening address with an invite for anyone to make the first speech. The first to stand was a Rune Priest of the Space Wolves known as Othere Wyrdmake.[2b]
Wyrdmake, as a psyker himself and as someone considered a respected colleague by Ahriman, may have been thought to have spoken out in defence of Librarians. Quite the opposite. Claiming knowledge of the Thousand Sons due to fighting alongside them on Shrike and Aghoru, he denounced each and every one of them as warlocks, deceivers and sorcerers, swearing the truth of the matter upon his oath of loyalty to Leman Russ. Malcador commented that this was a serious accusation, and asked if anyone would support it; Mortarion, primarch of the Death Guard legion stepped forth.[2d]
Mortarion repeated his charge that Magnus was a practitioner of sorcery. He illuminated his side of the debate by reminding the listeners of his personal experiences, and the worlds he had seen ruined by individuals who peered too long into dark places. He further reminded them all that Old Night was caused by psykers, their actions almost destroying the species. He pointed to the existence of the Sisters of Silence, an Imperial body specifically created to do the apparently essential job of not only guarding against the danger of psykers, but hunting them down. He dwelled upon horrific imagery he had seen, memories of sorcerous powers and the horrors they can conjure, and the power of such arcane barbarians to hold off or defeat Imperial purity. He closed by stating that he did not believe that Magnus was such a monstrous person as he had described and dealt with in his younger days...but that he was walking on the same path. Acknowledging his long-held anti-Librarian beliefs, he pressed that he was condemning Magnus not out of hate, but out of brotherly love and concern, so that Magnus may stop before it was too late.[2d]
Mortarion and Wyrdmake then invited chosen other speakers to the podium, where they made the case against Librarians for some three hours. After this, an interval took place before Magnus was scheduled to answer the accusations made against him.[2b]
The Testimony of the Crimson King
Magnus recounted many great deeds of Librarians, and pointed out that psykers were essential to the running of the Imperium, gesturing at the assembled astropaths to illustrate his point. He essayed that being fearful of the unknown was the mark of the ignorant and uneducated, ridiculous superstition, and that those without the courage to face new ideas sought to swamp them with scare-mongering. He pointed out that to people of previous historical periods, everything about a single individual at the Council would be regarded as magic, and that such long-ago people had beliefs that were proven wrong; the Sun does not orbit Terra after all, for example. He made an aside to Mortarion's testimony, claiming that the deepest desire leads to hate and lies, not love and concern.
He then spoke of he future; telling of what great deeds psykers can achieve and how much of a travesty the Council of Nikaea would be seen as by future Imperial citizens, as a barbarous event orchestrated by the ignorant. He refuted the claims against his legion, pointing out that the Thousand Sons fight at the forefront of the Great Crusade, taking the light of the Imperium to places others fear to tread and widening Imperial knowledge with their hunt for information. He then told a parable of men sitting around a fire in the dark of an underground cavern; one of their number discovers the light of outside, but his fellows are unwilling to believe him, content with the light from their fire. Wishing to illuminate his fellows, the explorer works hard, digging a great tunnel into the ceiling of the cavern and bringing the light to all his colleagues. That man knew he had to show his friends the truth, and strove to do so, despite their rejection and disbelief. Magnus claimed that in this case, the light is knowledge of the empyrean that he simply wanted to make available to everyone.[2d]
Magnus had spoken passionately with great power and the Council became even more divided. While effective, the Witch Hunters could not match Magnus' persuasiveness. The Council was once again adjourned. After the break, Magnus, who had felt that he had swayed many of those present with his testimony, was dismayed to pick up on a wide cloud of negative judgement now emanating from the Council, for reasons unknown to him, but perhaps having something to do with the events surrounding a servant of the Space Wolves...
Present amidst the concealed Space Wolves contingent - much to the consternation of Constantin Valdor - was Kasper Hawser, Skjald of Tra, or Third Company. The reason Valdor was perturbed by his presence was that Leman Russ had earlier made it clear to the Chief Custodian that the Space Wolves suspected that Hawser was a Hidden One of the Thousand Sons; a deep-cover intelligence agent who unaware of their own status as a scouting conduit. His presence in the command centre constituted a serious security risk, even with the psi-blocking skills of the Sisters of Silence and the inert materials used in the construction of the Nikaea complex. However, these factors were the very reasons that the Russ decided to explore the possibility that Hawser was a Hidden One. After his debrief, Hawser was committed to the supervision of a senior Custode, Amon Tauromachian, and allowed to watch the Council deliberate. It was during this time that the Thousand Sons made an apparent attempt to remove their apparently-compromised spy, as Amon , Master of the Hidden Ones and Equerry to Magnus the Red made a sorcerous attack on Amon Tauromachian and attempted to eliminate Hawser. Amon was driven off by the intervention of Bjorn of the Space Wolves, and the incident reported immediately; the Space Wolves fully under the impression that news of it would influence the judgement of the Emperor.
Tragically for everyone concerned, it would later be revealed that the 'Amon' that attacked Tauromachian and Hawser was not in fact Amon of the Thousand Sons, but an aspect of the Primordial Annihilator masquerading as the Master of the Hidden Ones as part of a convoluted scheme to remove the threat presented by both the Space Wolves and the Thousand Sons to the grand chaotic plan that would result in the Horus Heresy. The real Amon - and all the Thousand Sons present, including Magnus - had no idea of what had transpired in their names.
The Librarians Speak
As the end of the Council approached, Malcador arose, and asked if there were any remaining who would like to speak, before final judgement was made.
The tension could easily have been cut with a knife when a group of Space Marine Librarians stood and approached the dais. Malcador the Sigillite acknowledged them with a nod, and all fell silent. Among the group were some of the greatest Librarians of the Space Marine Legions. One of their number, a junior White Scars marine called Targutai Yesugei, spoke up, saying that there was nothing inherently evil about a Librarian. An Astartes psyker was akin to an athelete, a gifted individual who must be trained for the greatest results, or a bolter or Land Raider, a weapon that must be treated with respect and not loosed indiscriminately. They proclaimed that the best way forward would be to firm up the training of human psykers across the galaxy, and that this be made an Imperial priority, not their eradication; for with such a group of trained specialists loyal to the Emperor, the galaxy could be taken with ease. They also stated that any study of sorcery must of course be forbidden, effectively presenting a 'third way' to the Council. Some versions of the story of the Council claim that the Emperor immediately agreed to this proposal, as if waiting for it.[2d] However, other events, more believable in the light of what would transpire, are also presented.
According to the Grimoire Hereticus, a number of Librarians attempted to storm out of the hall after they were horrified of the reactionary as well as the misguided direction the debate was taking place.
The Emperor's Decision
Ultimately, in a speech to the gathered Astartes (which seemed to Azhek Ahriman to be directly intended for Magnus himself[2d]), the Emperor issued what would become known as the Edict of Nikaea, decreeing that the Legiones Astartes, beyond the use of Navigators and Astropaths, would no longer employ psykers. They were to disband their Librarius departments, the Librarians re-deployed to the battle companies and the primarchs themselves were to refrain from using any psychic powers they possessed. This of course applied to Magnus, whose use of sorcery was declared not proven. The Emperor also gave one final warning:
The Emperor was much enraged with Magnus personally. While he chose to refrain from outright announcing to the Council that Magnus was a sorcerer, the Emperor believed that Magnus had at least dabbled with the black arts. Seeing this as a personal betrayal - for the Emperor had, many years earlier, chosen to reveal secrets of the Warp to Magnus and Magnus alone - he issued his wayward son with a personal warning:
It is said that Magnus' face appeared as if made from brittle stone at hearing this proclamation, stone upon the edge of cracking. Nevertheless, he bowed his knee to his father and pledged to obey. It was a pledge he would not keep.
A listing of notable attendees other than the Emperor of Mankind. It should be noted that there were several individuals in attendance whose identity remains hidden. This is due to the use of "falsehoods" that hid the identities of the person, or persons concealed behind them. The Emperor ordered that falsehoods be used so that no individuals' testimony would "be corrupted by fear of those who's eyes are upon him." It is implied by Ahzek Ahriman of the Thousand Sons that the individuals behind the falsehoods were in fact Primarchs from other Legions.[2c][2d]
Aftermath and Effects
The Emperor's Decree would prove to be a severe handicap to the Loyalist legions that fought for him during the Horus Heresy. During the Battle of Calth, when the Word Bearers summoned hordes of daemons, Roboute Guilliman ruefully considered that Nikaea had deprived the Ultramarines of their best weapon against denizens of the Warp, the Librarius. Guilliman also resolved that, if they survived the battle, their first order of business would be to see the Decree abolished.
During the Battle, Nathaniel Garro, a loyalist Captain of the Death Guard, recruited Tylos Rubio, a former Codicier of the Ultramarines, on the orders of Malcador the Sigillite. Malcador later gave Rubio free reign to use his psychic abilities, but did not indicate whether this permission was a step towards abolishing the Decree altogether. Khorarinn, one of the Adeptus Custodes, warned Garro that he considered the Decree to be fully in effect, and threatened that he would execute Rubio instantly if the Ultramarine used his abilities in Khorarinn's presence.
Despite the Emperor's decision, in the aftermath of the Horus Heresy enforcement of Nikea ceased. By M41, the choice of whether to have Librarians was left to individual chapters. The Salamanders explained to the Marines Malevolent that they felt Nikea was outdated, while the Marines Malevolent retained a healthy distrust of psykers and Warp-seers.
Within the archives of the Blood Ravens, the title to this event is known as the Heart of the Thousands. Furthermore, the Apocrypha of Haidyes was used during the Hearing which later became the maxim of the Blood Ravens Chapter. 
A detailed explanation of the term "Trivia" and "Varia" as used in the Lexicanum can be found here.
- The name, subject, and consequences of the Council of Nikaea have strong resemblance to the Roman Council of Nicea in 325 AD, which helped shape Catholic dogma.
- 1:Index Astartes III, pgs. 41-3
- 2: A Thousand Sons (Novel) by Graham McNeill:
- 3: Collected Visions, pgs. 92-94
- 4: Prospero Burns (Novel) by Dan Abnett, Chapters Nine, Ten and Eleven
- 5: Know No Fear (Novel) by Dan Abnett, Ushkul//Thu, Chapter Two, pg. 349
- 6: Garro: Legion of One (Audio Book) by James Swallow, Track 7: The Lair of the Beast
- 7: Salamander (Novel) by Nick Kyme, Chapter Three, Part I, pg. 91
- 8: The Trials of Isador (Short Story) - Blood Ravens: The Dawn of War Omnibus by C.S. Goto, pgs. 270-272
- 9: Angel Exterminatus (Novel) by Graham McNeill, Chapter Four
- 10: Garro: Sword of Truth (Audio Book), by James Swallow, Track 5: The Dilemma