Roman Emperor Constantine was not the founder of Constantinople. The Megarians founded the city in 667 BC, and gave it the name Byzantium. The Greeks colonized the city from Megara in 657 BC. Byzantium was a Greek speaking city when Constantine built his imperial palace there in 324 AD, and renamed it Constantinople after himself. It subsequently became the capital of the Eastern Roman Empire but it continued to be a Greek speaking city till it was conquered by the Ottomans in 1453. The name “Byzantine Empire” was coined by historians after the fall of the Eastern Roman Empire.
By building his imperial palace in Constantinople, Constantine gave the city the status of the Roman Empire’s second capital. Since he had converted to Christianity in 312 AD, Constantinople became the center of Christian thought. Several Greeks converted to Christianity and they started applying to their new religion what they were good at: Athenian style philosophical disputation. The orientals in Constantinople, and in Syria, Egypt, and Mesopotamia, who were hellenized by their centuries of contact with the Greeks, joined the disputations. Eastern Christianity was divided by a series of antagonistic doctrines on matters of faith.
The first major theological dispute to emerge in Eastern Roman Empire was on the interpretation of Trinity. This dispute was mainly between Origen of Alexandria, Athanasius, and Arius. To resolve the dispute, Constantine called the First Ecumenical Council at Nicaea (325 AD), in which he upheld the doctrine of Trinity. Arius was branded as a heretic and sent to exile, but his doctrine survived among the Goths and Vandals till the eighth century.
In the fifth century, Nestorius, Patriarch of Constantinople, proposed the doctrine which overemphasized the humanity of Christ. The followers of the Antiochene school were already learning in that direction and Nestorius found support in several areas of the Levant. The Council of Ephesus in 431 AD denounced Nestorius as a heretic. He left Constantinople and established his Church in the Persian Empire (in Mesopotamia) where he was supported by the Persian King. The Nestorians gained influence in India, Turkestan, and China. The “one nature” doctrine of Monophysites took hold of a number of congregations in Egypt, Syria, and Anatolia. The Armenian Church sided with the Monophysites and ignored the Pope in Rome.
By the middle of the fifth century, the doctrinal disputes in Eastern Orthodoxy had become irreconcilable. The Roman Emperor could not engineer a reconciliation.
But despite the doctrinal disputes, Christianity kept spreading in the Eastern Roman Empire and even in the Persian Empire. Between the fourth and seventh centuries, thousands of monasteries came up in Constantinople, Egypt, Syria, Anatolia, and Mesopotamia. The teachings of Egyptian Saint Antony the Great (251 – 356 AD) on the standards of ascetic life was a major influence on these monasteries. He established the notion that the ascetics (monks) have to be celibate. Some resources have blamed the celibate ascetics for cutting into Roman demographics. But in his work of history, Edward Gibbon says that the celibate ascetics cannot be held responsible.
Constantine’s decision to make Constantinople the second capital of the Roman Empire led to a transformation of Christianity into a theological and disputative religion.