Byzantine Christianity

The Eastern Orthodox Church, also known as the Orthodox Church, or officially as the Orthodox Catholic Church, is the second largest Christian church and one of the oldest extant religious institutions in the world. The Eastern Orthodox Church teaches that it is the One, Holy, Catholic and Apostolic Church established by Jesus Christ in his Great Commission to the apostles. It practices what it understands to be the original Christian faith and maintains the sacred tradition passed down from the apostles.

The Eastern Orthodox Church is a communion of churches, each typically governed by a Holy Synod. It teaches that all bishops are equal by virtue of their ordination, and has no central governing structure analogous to the Papacy in the Roman Catholic Church. The contemporary Orthodox Church had shared communion with the Roman Catholic Church until the East–West Schism of AD 1054, which had been triggered by disputes over doctrine, especially the authority of the Pope. Prior to the Council of Chalcedon in AD 451, the Eastern Orthodox had also shared communion with the Oriental Orthodox churches, separating primarily over differences in Christology.

Eastern Orthodoxy spread throughout the Roman and later Eastern Roman (Byzantine) Empires and beyond, playing a prominent role in European, Near Eastern, Slavic, and some African cultures. During the first eight centuries of Christian history, most major intellectual, cultural, and social developments in the Christian Church took place within the Empire or in the sphere of its influence, where the Greek language was widely spoken and used for most theological writings. As a result, the term "Greek Orthodox" has sometimes been used to describe all of Eastern Orthodoxy in general, with the word "Greek" referring to the heritage of the Byzantine Empire. However, the appellation "Greek" was never in official use and was gradually abandoned by the non-Greek-speaking Eastern Orthodox churches, from as early as the 10th century A.D.

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