The Necromancy Ban of 3E 431 was enacted by the Mages Guild per the new Arch-Mage, Hannibal Traven. The Ban was to immediately remove all traces of Necromancy from the Mages Guild, though Necromancy itself remained legal in Cyrodiil. It was effective, for the most part, but dealt a serious blow to the Guild that would come back to haunt it.
In 3E 431, Hannibal Traven was named Arch-Mage of the Mages Guild. His first decree as Arch-Mage was to enact an all-consuming ban on the black art of Necromancy in the Guild. All manners of Necromancy were to be purged from the Guild, including those devoted to its practice. Prior to the ban, Necromancy had been accepted, but frowned upon within the Guild. In provinces such as Morrowind, where Necromancy was illegal, Guild mages practicing it were forced to operate out of sight and mind of the Morrowind government, as well as the Mages Guild. It is unknown if the Ban extended to the other provinces, or whether it was specific to Cyrodiil. What is known is that, in Cyrodiil, once the ban was posted, the Guild lost scores of mages. Half of the Council of Mages resigned in protest. Though the Guild continued to function without difficulty, it was severely weakened.
Arch-Mage Traven wrote a book, The Black Arts On Trial, which gave insight into his beliefs on Necromancy and his reasons for enacting the ban. In the book, Traven drew heavily on the old doctrines of both the Psijic Order and Vanus Galerion. Also, the book presented two Magisters of the Guild debating the issue, providing good reasons for and against Necromancy. The Magister for Necromancy, Ulliceta gra-Kogg, was later discovered to be a Necromancer herself. Traven still used her arguments in the book, and in the end drew the conclusion that "the risks of studying Necromancy outweigh its usefulness." On the basis that the Black Arts were corrupting and wicked in their nature, and that their use would pollute the Guild beyond recall, Traven banned the practice of Necromancy.
While at first the Ban seemed to have done little harm to the Guild, save decreasing its number, it would backfire on the Guild eventually. That backlash came in the form of the Order of the Black Worm, led by Mannimarco, King of Worms and Tamriel's most powerful Necromancer. Traveling to Cyrodiil, Mannimarco gathered to him the Mages that had been cast off by the Guild for their practice of Necromancy. He proceeded to launch an all out attack on the Mages Guild, with the intent of destroying the institution once and for all. Though the Attack was foiled by Arch-Mage Traven and his protege, the Champion of the Mages Guild, the Guild was left in a severely weakened state. Traven himself perished in the struggle.
Following his death, the Champion became the new Arch-Mage of the Mages Guild. The Champion did not, however, lift the Ban, possibly due to the horrors witnessed during the attack, and the fact that there were still vengeful Necromancers left from the Order of the Black Worm's collapse. Suffice to say, during and after the Attack, opinions on Necromancy were shifted to a more negative outlook.
- In The Elder Scrolls IV: Oblivion the Necromancy Ban is one of the key instigators of the Mages Guild questline. Mages in the Guild will talk about Traven's banning continually throughout the questline until the end.