East–West Schism
Claims of the See of Constantinople

In 330, Emperor Constantine moved the imperial capital to Byzantium, which later became Constantinople. The centre of gravity in the empire was fully recognised to have completely shifted to the eastern Mediterranean. Rome lost the Senate to Constantinople and lost its status and gravitas as imperial capital.

The bishop of Byzantium was under the authority of the metropolitan of Heraclea when Constantine moved there. Thereafter, the bishop's connection with the imperial court meant that he was able to free himself from ecclesiastical dependency on Heraclea and in little more than half a century to obtain recognition of next-after-Rome ranking from the First Council of Constantinople (381), held in the new capital. It decreed: "The Bishop of Constantinople, however, shall have the prerogative of honour after the Bishop of Rome; because Constantinople is New Rome", thus raising it above the sees of Alexandria and Antioch. This has been described as sowing the seed for the ecclesiastical rivalry between Constantinople and Rome that was a factor leading to the schism between East and West. The website of the Orthodox Church in America says that the Bishop of Byzantium was elevated to Patriarch already in the time of Constantine.

Disunion in the Roman Empire contributed to disunion in the Church. Theodosius the Great, who in 380 established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following the death of Theodosius in 395, the Empire was divided for the final time into western and eastern halves. In the 4th century, the Roman emperor (reigning in Constantinople) started to control the Church in his territory.

The patriarchs of Constantinople often tried to adopt a commanding position over the other patriarchs, provoking their resistance. For example, in 431 Patriarch Cyril of Alexandria impeached for heresy Patriarch Nestorius of Constantinople.

Alexandria's objections to Constantinople's promotion, which led to a constant struggle between the two sees in the first half of the 5th century, were supported by Rome, which proposed the theory that the most important sees were the three Petrine ones, of Rome, Antioch, and Alexandria, with Rome in the first place.

However, the power of the patriarch of Constantinople continued to grow. Eastern Orthodox state that the 28th canon of the Council of Chalcedon (451) explicitly proclaimed the equality of the Bishops of Rome and Constantinople, and that it established the highest court of ecclesiastical appeal in Constantinople. The patriarch of the imperial capital succeeded in his efforts to become the leading bishop in the Byzantine Empire: he "headed a vast curia and other bishops who resided in Constantinople constituted a permanent synod, which became the real governing body of the church ".

Patriarch John IV of Constantinople, who died in 595, assumed the title of "Ecumenical Patriarch".

The idea that with the transfer of the imperial capital from Rome to Constantinople, primacy in the Church was also transferred, is found in undeveloped form as early as John Philoponus (c. 490 – c. 570). It was enunciated in its most advanced form by Photios I of Constantinople (c. 810 – c. 893). Constantinople, as the seat of the ruler of the empire and therefore of the world, was the highest among the patriarchates and, like the emperor, had the right to govern them.
language:response_language[Spanish], punctuation:no_comma