Syria, Persia, Central Asia—there were churches at Merv, Herat, and Samarkand—and India had detached themselves on a similar score. These extremely interesting Asiatic Christians are known in history as the Nestorian Church, and their influence extended into China. The Egyptian and Abyssinian churches also detached themselves very early upon similarly inexplicable points. Long before this formal separation of the Latin and Greek-speaking halves of the main church, however, there was a practical separation following upon the breaking up of the empire. Their conditions diverged from the first. While the Greek-speaking Eastern Empire held together and the emperor at Constantinople remained dominant in the Church, the Latin half of the empire, as we have already told, collapsed, and left the Church free of any such imperial control. Moreover, while ecclesiastical authority in the empire of Constantinople was divided between the high-bishops, or patriarchs, of Constantinople, Antioch, Alexandria, and Jerusalem, authority in the West was concentrated in the patriarch, or Pope, of Rome. The Bishop of Rome had always been recognized as first among the patriarchs, and all these things conspired to justify exceptional pretensions upon his part to a quasi-imperial authority. With the final fall of the Western Empire, he took over the ancient title of pontifex maximus which the emperors had held, and so became the supreme sacrificial priest of the Roman tradition. Over the Christians of the West his supremacy was fully recognized, but from the beginning it had to be urged with discretion within the dominions of the Eastern emperor and the jurisdictions of the other four patriarchs.
Ideas of worldly rule by the Church were already prevalent in the fourth century. Saint Augustine, a citizen of Hippo in North Africa, who wrote between 354 and 430, gave expression to the developing political ideas of the Church in his book The City of God. The City of God represents the possibility of making the world into a theological and organized Kingdom of Heaven. The city, as Augustine puts it, is "a spiritual society of the predestined faithful," but the step from that to a political application was not a very wide one. The Church was to be the ruler
- E. B. (quoted from Tröltsch).