The churches founded by the Apostles themselves include the Patriarchates of Alexandria, Antioch, Jerusalem, and Rome and Constantinople. The Church of Alexandria was founded by St. Mark, the Church of Antioch by St Paul, the Church of Jerusalem by Ss. Peter and James, the Church of Rome by Ss. Peter and Paul, and Church of Constantinople by St Andrew. Those founded in later years through the missionary activity of the first churches were the Churches of Sinai, Russia, Greece, Serbia, Serbia, and many others.
Each church has always had independent administration, but, with the exception of the Church of Rome, which finally separated from the others in the year 1054, are united in faith, doctrine, Apostolic tradition, sacraments, liturgies, and services. Together they constitute what is called the “Orthodox Church,” literally meaning “right worship,” derived from two Greek words: orthos, “right,” and doxa, “worship.”
The Orthodox Church historically stands in direct continuity with the earliest Christian communities founded in regions of the Eastern Mediterranean by the apostles of the Lord Jesus.
The destiny of Christianity in those areas was shaped by the transfer in 320 AD of the imperial capital from (Old) Rome to (New “Rome”) Constantinople by Constantine I.
As a consequence, during the first eight centuries of Church history, most major cultural, intellectual, and social developments in the Christian church also took place in that region; for instance, all ecumenical councils of that period met either in, or near Constantinople.
Missionaries, coming from Constantinople, converted the Slavs and other peoples of Eastern Europe to Christianity (Bulgaria, 864; Russia, 988) and translated the Scriptures and liturgical texts into the vernacular languages used in the various regions. Thus, the liturgy, traditions, and practices of the church of Constantinople were adopted by all and still provide the basic patterns of contemporary Orthodoxy.
Developments were not always consistent with the evolution of Western Christianity, where the bishop of Rome, or pope, came to be considered the successor of the apostle Peter and head of the universal church by divine appointment. Eastern Christians were willing to accept the pope as the first among equals, but not as the vicar of Christ, having authority over the other patriarchs.
This difference explains the various incidents that grew into a serious estrangement. One of the most vehement disputes concerned the filioque clause of the Nicene Creed (i.e., “and the Son”), which the Western church added unilaterally to the original text.
The schism came slowly. The first major breach came in the ninth century when the Pope refused to recognize the election of Photius as patriarch of Constantinople. Photius in turn challenged the right of the papacy to rule on the matter and denounced the filioque clause as a Western innovation.
The growing disputes between East and West reached another peak in 1054 AD, when mutual anathemas were exchanged. The sacking of Constantinople by the Fourth Crusade (1204 AD) intensified Eastern hostility toward the West.
Attempts at reconciliation at the councils of Lyon (1274 AD) and Florence (1438-39 AD) were unsuccessful. When the papacy defined itself as infallible (First Vatican Council, 1870 AD), the gulf between East and West grew wider. Only since the Second Vatican Council (1962-65) has the movement reversed, talks are bringing serious attempts at mutual understanding.
Regardless, the bishops of the Orthodox Churches trace unbroken succession to the very apostles themselves, therefore ultimately receiving their consecrations from our Lord Jesus Christ. Nothing is added to or subtracted from that deposit of faith which was "handed once for all to the saints" (Jude 3). Its primary statement of faith is the Nicene Creed
Adapted from OrthodoxWiki.