By the early fourth century, the Roman Empire was in decline, and so was its religion. One reason the Emperor Diocletian persecuted Christians was his belief that they were responsible for this decline. His successor was Constantine, who made Christianity the official imperial religion in 313 with the Edict of Milan.
Some historians argue that Constantine was an opportunist who saw the network of Christians as a powerful tool for unifying his faltering Empire. Whatever Constantines reasons, he changed Christianity from a persecuted, struggling church to a powerful imperial institution. Christianity became as compulsory as the Roman religion had previously been. Now many non-Christians were denied rights or persecuted, and some Christians holding other beliefs--heretics--were exiled. Constantine built huge, elaborate churches throughout his Empire, establishing worship services that were long, formal, and reminiscent of court rituals.
Bishops became powerful political figures as well as religious leaders, especially in the great imperial cities of Constantinople, Alexandria, Antioch, and Rome.
Constantine built a new capital, named after himself, on the site of the small, ancient city of Byzantium. Since he preferred Constantinople over Rome as his imperial capital, it quickly became the seat of power and court favor in the East. Its bishop was usually appointed by the Emperor and was closely associated with his favor. The rise of the See* of Constantinople as a church power challenged the traditional church powers, especially Alexandria in the East and Rome in the West.
calling the Council of Nicea in 325, Constantine declared
Constantinople the "Second Rome," and its bishop second
in rank only to the Bishop of Rome, despite the greater antiquity
and apostolicity of sees like Antioch and Jerusalem as well as
Alexandria. Some of their bishops resented Constantinople as a
result. As Emperor, Constantine was interested in preserving
peace more than in doctrinal details, and he gave his support