See of Nicomedia

The Metropolis of Nicomedia (Greek: Μητρόπολις Νικομηδείας) was an ecclesiastical territory (metropolis) of the Ecumenical Patriarchate of Constantinople in northwestern Asia Minor, modern Turkey. Christianity spread in Nicomedia already in the 1st century AD. Following the capture of the city by the Ottoman Turks in the early 14th century, the metropolitan see remained for a period vacant. The metropolis was re-established during the 15th century and remained active until the Greek-Turkish population exchange of 1922–1923.

Christianity spread to Nicomedia during the middle of the 1st century, while the city became the oldest bishopric established in the region of Bithynia, in northwestern Asia Minor. According to the Christian tradition, the first bishop was Prochorus, one of the Seven Deacons.

Nicomedia became a significant important administrative center during the reign of Emperor Diocletian. The latter aimed at transforming the city into a new capital of the Roman Empire. In 303, during the reign of the same emperor, the Christians of Nicomedia witnessed persecution, while another wave of persecution against the Christians occurred in 324 under Licinius. The number of the local Christian victims has not been estimated but it is believed that they were thousands. Among the martyrs were the legionaries Dorotheus, Gorgonius, Panteleemon and George, as well as the local bishop Anthimus. In 337 bishop Eusebius of Nicomedia baptised Emperor Constantine the Great on his deathbed.

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