In a dramatic move that would have lasting repercussions for the Christian world, three Roman legates, headed by Cardinal Humbert of Silva Candida, entered Hagia Sophia in Constantinople on a Saturday afternoon. Their aim was to settle ongoing theological disputes and assert the primacy of the papacy over the Eastern Orthodox churches. Amidst the rich Byzantine liturgy, the legates placed a papal bull of excommunication on the altar, directly challenging Patriarch Michael I Cerularius and the authority of the Eastern Church. This act of placing the bull, which bore questionable validity, was a declaration that sealed a schism which had been evolving through centuries of religious and cultural differences.

The backdrop of this event involved numerous theological disagreements, such as the use of leavened versus unleavened bread in the Eucharist and diverging beliefs regarding the authority of the pope. The excommunication was not immediate; it was a culmination of persistent tensions that had festered due to differing liturgical practices and political aspirations. Michael Cerularius retaliated by excommunicating the legates, and both sides remained firm in their positions, leading to a complete division between the Roman Catholic and Eastern Orthodox churches that persists to this day.

The act was not simply a local quarrel; it symbolized a growing rift that reflected deeper cultural, social, and political divides within Christendom. The legates' actions and the response from the Eastern patriarch laid the foundation for centuries of estrangement and hostility, profoundly altering the landscape of Christianity. This ecclesiastical split was a decisive moment, highlighting and concretizing existing fissures in the fabric of Church unity.