Summary
Papal legates laid a sentence of excommunication on the altar of Hagia Sophia against Patriarch Michael Cerularius, who answered in kind. Long-growing differences over papal authority, the Western addition of the filioque to the Creed, and practice hardened into a lasting division between the Roman Catholic Church and the Eastern Orthodox churches. It split the institutional church of the old empire into Latin and Greek halves; it was not a division of Christ's churches.