text: A letter heavily citing the Donation of Constantine helped contribute to this event, which was nearly avoided after a pair of meetings at Lyon.
full_question: A letter heavily citing the Donation of Constantine helped contribute to this event, which was nearly avoided after a pair of meetings at Lyon. Michael Cerularius was excommunicated by Cardinal Humbert, prompting this event. This event was ostensibly caused by a disagreement between the use of levened and unlevened bread and the mutual decleration of anathama made undoing this event nearly impossible, even though that decleration was revoked by Pope Paul VI in 1965. One side in this conflict cited Constantine relocating the capital to Byzantium as evidence for the Sea of Constantinople while the other side, led by Leo IX, cited several Ecumenical councils as evidence for the Sea of Rome. For ten points, name this 1054 event that split the church into eastern and western factions.
first_sentence: A letter heavily citing the Donation of Constantine helped contribute to this event, which was nearly avoided after a pair of meetings at Lyon.