1054 East–West Schism of the Christian Church

Timeline

1. 1053–1054Rome and Constantinople · ChristendomPope Leo IX dispatched legates to Constantinople to clash fiercely with Patriarch Cerularius over issues including papal primacy, the Filioque clause, the use of unleavened bread in the Eucharist, and the jurisdiction of the Bulgarian church; each side accused the other of heresy and negotiations broke down.
2. 1054Hagia Sophia · IstanbulCardinal Humbert and two colleagues placed the bull of excommunication on the altar before the Hagia Sophia, declaring Patriarch Cerularius and his followers excommunicated, accusing them of altering the Creed and rejecting Roman authority.
3. 1054Constantinople · Marmara RegionCerularius convened a synod and declared a counter-excommunication against Humbert and the other Roman legates, breaking off communion between the two sides. Although Leo IX and Cerularius both died shortly afterward, the mutual excommunications were never revoked and the East–West schism became formal.