From the schism to the Reformation
A major factor in the consolidation and expansion of Christianity in the West was the growth in the prestige and power of the bishop of Rome. Pope Leo I the Great made the primacy of the Roman bishop explicit both in theory and in practice and must be counted as one of the most important figures in the history of the centralization of authority in the church. The next such figure was Gregory I the Great, whose work shaped the worship, the thought, and the structure of the church as well as its temporal wealth and power. Although some of Gregory’s successors advocated papal primacy, it was the popes of the 11th century and thereafter who sought to exploit claims of papal authority over the church hierarchy and over all Christians.
Even while still a part of the universal church, Byzantine Christianity had become increasingly isolated from the West by difference of language, culture, politics, and religion and followed its own course in shaping its heritage. The Eastern churches never had so centralized a polity as did the church in the West but developed the principle of the administrative independence or “autocephaly” of each national church. During the centuries when Western culture was striving to domesticate the German tribes, Constantinople, probably the most civilized city in Christendom, blended classical and Christian elements with a refinement that expressed itself in philosophy, the arts, statecraft, jurisprudence, and scholarship. A thinker such as Michael Psellus in the 11th century, who worked in several of these fields, epitomizes this synthesis. It was from Byzantine rather than from Roman missionaries that Christianity came to most of the Slavic tribes, including some who eventually sided with Rome rather than Constantinople; Byzantium was also the victim of Muslim aggressions throughout the period known in the West as the Middle Ages. Following the pattern established by the emperors Constantine and Justinian, the relation between church and state in the Byzantine empire coordinated the two in such a way as to sometimes subject the life and even the teaching of the church to the decisions of the temporal ruler—the phenomenon often, though imprecisely, termed caesaropapism.
All these differences between the Eastern and Western parts of the church, both the religious differences and those that were largely cultural or political, came together to cause the schism between the two. The break in 1054 was followed by further evidences of alienation—in the 13th century, in the sack of Constantinople by Western Christians in 1204 and the establishment of the Latin patriarchate there; and in the 15th century, after the failure of the union of Florence and after the fall of Constantinople to the Turks in 1453.