schism · 1054 · Constantinople
On 16 July 1054 Cardinal Humbert laid a bull of excommunication against the patriarch Michael Cerularius on the altar of Hagia Sophia; on the 24th Cerularius' synod anathematized the legates in return. The anathemas were personal, and few that year thought the breach final — but after centuries of drift over the filioque, the azymes and jurisdiction, 1054 became the emblem of a separation not yet healed.
Legates in Constantinople to settle the azymes dispute and secure an alliance — met by a patriarch who would not bend.
Mutual anathemas, personal in law but final in memory: 1054 became the emblem of the East–West separation.