Byzantine church

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 contemporary 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.