Great Schism between Rome and Constantinople

July 16, 1054

A papal legation led by Cardinal Humbert of Silva Candida strode into Hagia Sophia during the liturgy and slapped a bull of excommunication on the high altar, then walked out. The patriarch returned the favor. A rift over unleavened bread, papal primacy, and the filioque became permanent alienation. The mutual excommunications would not be formally lifted until Pope Paul VI and Patriarch Athenagoras met in 1964.