Great Eastern Schism

The East–West Schism, also called the Great Schism and the Schism of 1054, was the break of communion between what are now the Eastern Orthodox and Roman Catholic churches, which has lasted since the 11th century. It is not to be confused with the Western Schism which lasted from 1378 to 1417 (which is also sometimes called the "Great" Schism).

A succession of ecclesiastical differences and theological disputes between the Greek East and Latin West pre-dated the formal rupture that occurred in 1054. Prominent among these were the issues of the source of the Holy Spirit, whether leavened or unleavened bread should be used in the Eucharist, the Bishop of Rome's claim to universal jurisdiction, and the place of the See of Constantinople in relation to the Pentarchy.

In 1053, the first step was taken in the process which led to formal schism: the Greek churches in southern Italy were forced either to close or to conform to Latin practices. In retaliation, the Ecumenical Patriarch of Constantinople Michael I Cerularius ordered the closure of all Latin churches in Constantinople. In 1054, the papal legate sent by Leo IX travelled to Constantinople for purposes that included refusing to Cerularius the title of "Ecumenical Patriarch" and insisting that he recognize the Pope's claim to be the head of all the churches. The main purpose of the papal legation was to seek help from the Byzantine Emperor in view of the Norman conquest of southern Italy and to deal with recent attacks by Leo of Ohrid against the use of unleavened bread and other Western customs, attacks that had the support of Cerularius. Historian Axel Bayer says the legation was sent in response to two letters, one from the Emperor seeking assistance in arranging a common military campaign by the eastern and western empires against the Normans, and the other from Cerularius. On the refusal of Cerularius to accept the demand, the leader of the legation, Cardinal Humbert of Silva Candida, O.S.B., excommunicated him, and in return Cerularius excommunicated Humbert and the other legates. This was only the first act in a centuries-long process that eventually became a complete schism.

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