Roman and Byzantine Empire

Christianity spread rapidly over the first three centuries aided by the relative internal peace of the Roman Empire. There is no evidence about the status of the pope in the earliest days of the church: he was accorded special honor as the successor of St. Petersaint peter is acknowledged, but to the bishop of Rome was accorded honor over the other bishops, not authority in general. During this period of first organization the Christian Church had to deal mainly with occasional, but sometimes severe persecutions under Roman emperors such as the one organized by Nero, who accused the Christians of the fire took place in Rome on July 19th, 64; during this persecution, the apostles St. Peter and St. Paul died as martyrs. To preserve the bodies for resurrection, Christians started burring of the dead in safe place: the catacombs.

In the meantime, a church hierarchy emerged: the Bishops of Alexandria, Antioch and Rome assumed the title Patriarch.

New great persecution of Christians took place during the Empires of Decius (251), Diocletian (303), and Galerius. Galerius, on his death bed, signed the Edict of Galerius, allowing Christians freedom to practice their religion without hindrance. Then, Roman Emperor Constantine was converted in 312 and with his Edict of Milan (313) made the state neutral with regard to religion at the beginning, and then supporting the new religion as a mean to control the Empire. Following this line, Constantine called and took part to the First Ecumenical Council of Nicaea in 325, first example of Caesaropapism, with the Byzantine Emperor exerting various degrees of influence over the Church.

The moving of the capital to Constantinople in 330 left Rome as the see of the Pope, the Bishop of the city. From the point of view of the terms, "Pope" is the name of the lead bishop in a major patriarchate, like the original Patriarchs of Jerusalem, Antioch, Constantinople, Rome, or Alexandria. Due to the progressive splitting of the churches following the First Council of Nicaea, the First Council of Constantinople, the Council of Ephesus and the Council of Chalcedon, the more term Patriarch is mainly related to the leading Orthodox bishops, in order to distinguish them from the Pope in Rome.

Persecution was briefly revived during the reign of Julian the Apostate (361-363) who tried to restore paganism to the empire, but in Thessalonica Christianity was made the official religion of the Empire by Theodosius in 380.