The Edict of Nikea forced the legions to ban the biggest threat to the forces of chaos and ensured the thousand sons eventual turn, as, in a typically stupid short sighted move by the emperor he banned the use of Psychic powers other then Astropaths and Navigators.

I know that during the time of the Heresy the edict was instigated to different levels by the loyal forces. Guilliman states at Calth that his first act after the war will be to ensure his father lifts the ban, the Darkangels also lifted the ban during the Heresy, Corax flip flopped, the space wolves don't have psykers (just like they don't have wolves on Fenris) but the Imperial Fists, in typical fashion locked theirs up and decided they could meditate the psyker away.

But when was the ban officially lifted, when where the legions and later chapters allowed to use Psykers again without fear of reprisal? Did the Emperor lift it prior to the Seige of terra, or was it done post golden throne internment? Or was it never truly ended, everyone just ignored it understanding that Psykers where a necessary evil in the fight against chaos?

  • As for deciding whether the Council of Nikea was engineered by Chaos Gods or a bad decision from the Emperor, the article on Lexicanum says "Guilliman noted that the timing was so convenient that it almost seemed like someone had planned it" with a reference to the novel Know no Fear and a link to Tzeentch's article. As I didn't read that book, I don't know if this can be trusted.
    – Taladris
    Commented Jun 5, 2019 at 11:17
  • The same article says that "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." (unsourced claim). But I believe this is just a hint that there is no source in canon about abrogation/non-enforcement of Nikea post-heresy
    – Taladris
    Commented Jun 5, 2019 at 11:22
  • I was wondering if anything in the fluff had mentioned it yet, if not I imagine it will be coming later in the series. Possibly during the post heresy set of books where the legions deal with the aftermath of the war and Guilimon splits them into chapters.
    – Richard C
    Commented Jun 5, 2019 at 13:55

1 Answer 1


It wasn't officially lifted before the Siege of Terra and slightly modified afterwards:

Malcador the Sigillite acting with Emperor's authority gave permission for the Knights-Errant (a newly created chapter made mostly of the loyal members of the traitor legions,) a permit to use psykers. A similar permit was given to Space Wolves to use their "Rune Priests".

In practice, by the time of the Battle of Terra only Imperial Fists and Raven Guard officially had no librarians- Dorn locked his ones up in the Phalanx (but he was apparently ready to use them when they were needed) and Corax felt guilty after initially ignoring the decree, so he ordered (however few he had left) librarians to rejoin the ranks as common soldiers (kudos @RichardC). Rest of the primarchs sooner or later decided that it is really stupid to stop using the most effective weapon against the enemy and decided to go against the decree.

After the Battle, a compromise has been achieved: while educating psykers for the purpose of serving mankind is allowed, studying warp sorcery is treated as a heresy. Still, there are a few chapters (i.e. Black Templars) that uphold the original Emperor's order and not allow any Librarians among their Marines.

Sources: Council of Nikea, history of Librarians

  • Corax had Libraians post the massacre, in the Corax Anthology series he is shown having lifted the ban allowing them to scrye and support the Ravenguard. Towards the end of the book however his guilt at all he has done leads him to once again ban the Libraians, forcing them to rejoin the ranks swearing to never use there abilities. he then sends his chief librarian Balsar Kurthuri back to confess to Malcador and his father and determine if there should be a penance paid.
    – Richard C
    Commented Jun 6, 2019 at 10:06
  • @RichardC I've updated my answer. I just knew he had no psykers, but didn't know the reasons.
    – Yasskier
    Commented Jun 6, 2019 at 20:28

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