The schism between Rome and Constantinople which divided the Church in 1054 had a 600 years old history. Already in the fourth century the emperor Constantine had selected the city of Byzantium as the new capital of the Roman Empire. He renamed the city after himself, Constantinople, meaning the city (Greek polis) of Constantine. Initially it was the sole capital of the Empire. However, soon after his death in 337 it became clear that the Empire was too vast, and Constantinople too far to the East, for this city to be the only capital. Rome was restored as a capital city for the western half of the Empire, while Constantinople remained the capital of the Eastern half. The division followed the linguistic divide within the Empire, between the Greek-speaking eastern half and the Latin-speaking western half. The situation received a new twist in the fifth century, when the barbarian invasions destroyed the Roman Empire in the west but Constantinople and the eastern half of the Empire survived the onslaughts. Then the balance shifted again. The barbarian tribes converted to Christianity and injected new life into western Christendom, while eastern Christendom was threatened by the emerging power of Islam. Muslim armies in the seventh century captured the cities of Alexandria, Antioch, and Jerusalem. As a result, only two of the five patriarchal sees retained effective freedom for governing the Church: Rome and Constantinople.

From the fifth century on, the gap between the Latin and the Greek churches went on increasing for various reasons – political, cultural and dogmatic. Politically the west became increasingly independent and the Popes seemed to support this process by restoring the Empire in the west. Culturally, the two languages, Latin and Greek, alienated each other making communication difficult. There were also serious liturgical and doctrinal differences. At the same time, the churches also displayed a sense close unity, especially when it came to essential matters of the faith, as was the case with the ecumenical councils which defined the main dogmas of the faith. For example, at the crucial Council of Chalcedon both the churches were united against the heretics, but in the aftermath there also emerged a short schism of forty years between Rome Constantinople from 482 to 519, known as the Acacian schism when Rome broke off communion with Constantinople because the Popes felt that Constantinople was challenging the integrity of the Council of Chalcedon. Eventually communion was restored and the churches continued to cooperate with each other.

But there were irritating incidents happening intermittently. One such was the introduction of the Filioque clause – adding the Son to the Father in the procession of the Holy Spirit – into the Nicene creed by the Council of Toledo in 589. The clause received wider acceptance in the West through its adoption in 794 by the Council of Frankfurt, which was convoked by the Emperor Charlemagne. As at Toledo, the addition at Frankfurt was intended only for the West, in order to counter residual Arianism. Nevertheless its introduction offended the East. As well as various theological objections, there was the procedural point that the East was unilaterally tampering with a text approved by an Ecumenical Council. The papacy was initially reluctant to countenance the Filioque clause, but gradually became an advocate of the change. As a result, the issue of papal authority also entered the debate. Was the Pope superior to an Ecumenical Council, with authority to alter its doctrinal decrees? Papal authority of this kind was quite unacceptable to the church of Constantinople.

The crowning of Charlemagne as Emperor by Pope Leo III on Christmas day 800 in Rome also irritated Byzantium. There it was felt that with the collapse of the western Empire in the fifth century through the barbarian invasions, only the ruler of the eastern Empire could truly claim the title of Emperor. Charlemagne might be considered a king but not an Emperor. That the Pope had been responsible for this unwelcome act led to some distancing from Rome on the part of eastern Christians, to their looking more to the patriarch of Constantinople as the one and only head of their church. But in spite of all these, communion between the two churches remained (to be continued).