July 16, 1054: Liturgical, linguistic, and political divisions cause a permanent split between the Eastern and Western Churches, known as the East–West Schism or the Great Schism. The three legates, Humbert of Mourmoutiers, Frederick of Lorraine, and Peter, Archbishop of Amalfi, entered the Cathedral of the Hagia Sophia during mass on a Saturday afternoon and placed a papal Bull of Excommunication on the altar against the Patriarch Michael I Cerularius. The legates left for Rome two days later, leaving behind a city near riots.