New Rome and the Seat of a Patriarchate

Constantine chose the old Greek trading city of Byzantium for his new capital largely for its defensible position on a peninsula between the Bosphorus and the Golden Horn, and dedicated it in 330 CE with ceremonies that mixed pagan and Christian elements, a reflection of an empire only beginning its official turn to Christianity. He styled the city Nova Roma, New Rome, and it grew quickly into the wealthiest and most populous city in the Christian world, its bishop gaining a rank, confirmed at the First Council of Constantinople in 381 CE, second only to Rome itself. Over time the see became the Ecumenical Patriarchate, recognized among the Eastern Orthodox churches as first among equals, a position of honor rather than of the direct jurisdiction a pope holds over Roman Catholicism.

The city hosted two of Christianity's seven ecumenical councils under its own name and lived through the Iconoclast controversy of the eighth and ninth centuries, when a succession of emperors banned the veneration of religious images as idolatrous, provoking fierce resistance from monks and much of the wider church before icon veneration was formally restored in 843 CE. Hagia Sophia, completed under Justinian in 537 CE as the Patriarchate's cathedral, stood at the center of that struggle and of the city's ceremonial life more broadly, its own detailed history recorded separately.