St. Eirene Church, 4th-century Constantinople

Built by Constantine in 324 on the site of the Greek city Byzantium and capital of the eastern empire from 330, this city was intended to be a new Rome. It remained, with a brief interruption, the capital of the eastern empire until 1453 when it fell to the Turks. Byzantium had a Christian community from the second century. After the city’s construction and designation as capital, Constantinople rose in importance in the eastern church. It became a patriarchate in 383 and after 451 was designated second only to Rome in importance. This took place over the objection of the pope and competition for preeminence between the two sees was a factor contributing to the eventual division of the eastern and western churches. The patriarch of Constantinople is to the present considered the "Oecumenical Patriarch" of the eastern orthodox churches.