Linguistic and cultural differences, as well as political events, contributed to the estrangement.From the 4th to the 11th century, Constantinople (now Istanbul), the centre of Eastern Christianity, was also the capital of the Eastern Roman, or Byzantine, Empire, while Rome, after the barbarian invasions, fell under the influence of the Holy Roman Empire of the West, a political rival.In practice, the emperor had the upper hand over much of church administration, though strong patriarchs could occasionally play a decisive role in politics: Nicholas I (byname Nicholas Mystikos; patriarch 901–907, 912–925) and Polyeuctus (patriarch 956–970) excommunicated emperors for uncanonical acts.
The Church of the Holy Wisdom, or Hagia Sophia, built by Justinian in the 6th century, was the centre of religious life in the Eastern Orthodox world.
It was by far the largest and most splendid religious edifice in all of Christendom.
Its adherents live mainly in the Balkans, the Middle East, and former Soviet countries.
(“right believing”) has traditionally been used in the Greek-speaking Christian world to designate communities or individuals who preserved the true faith (as defined by those councils), as opposed to those who were declared heretical.
Several of the autocephalous churches are de facto national churches, the Russian church being by far the largest.
However, it is not the criterion of nationality but rather the territorial principle that is the norm of organization in the Orthodox church.
Although it has provoked controversy, the establishment of the autocephalous At the beginning of the 2nd millennium of Christian history, the church of Constantinople, capital of the Eastern Roman (or Byzantine) Empire, was at the peak of its world influence and power.
Neither Rome, which had become a provincial town and its church an instrument in the hands of political interests, nor Europe under the Carolingian and Ottonian dynasties could really compete with Byzantium as centres of Christian civilization.
Virgin Mary (centre), holding the Christ Child, Justinian (left), holding a model of Hagia Sophia, and Constantine (right), holding a model of the city of Constantinople; mosaic from Hagia Sophia, Istanbul, 9th century. He held the title of “ecumenical patriarch,” which pointed to his political role in the empire.