The Schism of 1054

On 16 July 1054 the legates of Pope Leo IX laid on the altar of Hagia Sophia a bull excommunicating Patriarch Michael Cerularius; the patriarch replied by anathematizing the legates. Contemporaries did not see this as a final break.

Historians point to differences in theology (the Filioque), church order (papal primacy), rites (unleavened bread), as well as political and cultural factors. The sack of Constantinople by the Crusaders in 1204 made the estrangement irreversible.

The anathemas of 1054 were mutually lifted in 1965 by Patriarch Athenagoras and Pope Paul VI, but eucharistic communion has not been restored. This account follows the academic consensus; assessments of individual events differ between sources.