Ideas · 1054 CE
The East–West Schism
Hagia Sophia, Constantinople (Istanbul, Türkiye)
On 16 July 1054 papal legates led by Cardinal Humbert laid a document excommunicating Patriarch Michael Cerularius on the altar of Hagia Sophia in Constantinople; days later the patriarch's synod excommunicated the legates in return. The quarrel capped centuries of disputes over the pope's authority, the filioque wording of the Nicene Creed and whether the Eucharist should use leavened or unleavened bread.
Why it mattered
The break, hardened when crusaders sacked Constantinople in 1204, divided Christianity into a Roman Catholic West and an Eastern Orthodox East; the mutual excommunications were lifted only in 1965.
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