Christendom East and West. In the early centuries of Christianity the Church was governed by local bishops. Each community over which a bishop presided was jurisdictionally independent from the rest, but they were all regarded as part of a single, united body of Christ. The five most important episcopal sees were in Rome, Constantinople, Alexandria, Antioch, and Jerusalem, with the bishops of these cities taking on the title of patriarch. After the spread of Islam in the eighth century the balance of ecclesiastical power was upset: the churches of North Africa and the Middle East lost much of their influence, and only the patriarchates of Rome and Constantinople remained as great centers of Christendom. When Charlemagne was crowned Holy Roman Emperor in 800 the situation became more polarized. Not only were there two religious centers within the Christian world, but two rival empires...