With the Great Schism of July 16, 1054, the Christian Church split into the Catholic Church and the Orthodox Church. In the 4th Century AD, ruling the Roman Empire was a difficult task. Great differences among its various populations made the territory hard to manage. In 395 emperor Theodosius I divided the empire in two: the Western Roman Empire, with Rome as its capital; and the Eastern Roman Empire, the capital of which became Constantinople. Initially this division only concerned the administration of political power, but later it would extend to other aspects as well. Different languages were spoken in the two empires, making communication increasingly difficult. The separation of the two Empires soon applied to religious, or spiritual power as well. The Roman Pope was the supreme leader of the Christian Church. But over time the Patriarch of Constantinople, the highest Christian authority in the Orient, became increasingly intolerant of the Pope’s supremacy, and the Eastern Roman Empire began to demand greater independence in the religious sphere as well. Priestly celibacy, the liturgy, and the management of temporal power were all issues that the Patriarch of Constantinople wanted to command with the same authority as the Pope.
People in the Roman Pope’s territory spoke Latin, and their lands were divided and weakened by frequent barbarian raids.
By contrast, the Eastern territories ruled by the Constantinople Patriarch spoke Greek, and were united and experiencing prosperous growth. And so in 451 the Christian bishops of the East and West held a Council in the city of Chalcedon to resolve the crisis. The Council ruled that the Churches of Rome and Constantinople were equally important. It was a revolutionary decision. Pope Leo I refused to accept it, but the Schism had begun. Over the following six centuries, the separation widened. The two Christian churches began to lead independent lives and adopt different doctrines. The final division took place following a disagreement over dioceses in Southern Italy. At the beginning of the year 1,000, Southern Italy was still divided into territories belonging to the Church of Constantinople, and others that belonged to Rome. In July 1054, Pope Leo IX sent a delegation to the court of the Patriarch of Constantinople Michael I Cerularius to attempt to reach an agreement. But the two sides failed to find common ground. Leo IX excommunicated Cerularius. Cerularius, in turn, excommunicated the Roman Pope. Christianity was now officially split in two: the Catholic Church in the West [katholikòs = universal] and the Eastern Orthodox Church in the East The Roman Catholic Church and the Eastern Orthodox Church remain divided today.