His disputes with Pope Leo IX over church practices in the 11th century played a role in the events that led to the Great Schism in 1054.

[4] Pope Leo IX assured Michael I that the donation was completely genuine, not a fable or old wives' tale,[citation needed] arguing that only the apostolic successor to Peter possessed primacy in the Church.

[5] In spite of this, they decided to proceed with their mission, but even before any religious discussions were held, problems arose regarding some basic formalities and ceremonies.

During that time, from April to July 1054, Cardinal Humbert and his colleagues continued with their activities in Constantinople, taking part in informal religious discussions on various issues.

Despite the fact that their legatine authority officially ceased after the pope's death, Cardinal Humbert and his colleagues decided to engage in open dispute with the patriarch.

On the same day, Cardinal Humbert and his colleagues entered the church of the Hagia Sophia during the divine liturgy and placed the charter on the altar.

[7][8] Only the three men were anathematised, and a general reference was made to all who support them - there was no explicit excommunication of the entire Western Christianity, or of the Church of Rome.

[9] Although the excommunication delivered by Cardinal Humbert was invalid, the 1965 gesture represented a significant step towards restoring communion between Rome and Constantinople.

Michael I apparently planned a rebellion, intending to overthrow Isaac I and claim the throne for himself or for his relative Constantine Doukas.