Metropolis of Nicaea

The First Ecumenical Council was held in the city in 325, and under Emperor Valens (r. 364–378), the local see was removed from the purview of its neighbour and rival, Nicomedia, and raised to the status of a separate metropolis.

[2] In the Notitiae Episcopatuum from the 8th to the 15th centuries, Nicaea steadily occupies the eighth place in the metropolitan sees subject to the Patriarchate of Constantinople.

Apart from the desire to maintain in existence historical and prestigious sees like Nicaea, this practice was most likely the result of their proximity to the seat of the Patriarchate in Constantinople, which allowed their bishops to both administer their dioceses and play an active role in the central administration of the Church.

[5] Nevertheless, as a result of the scarcity of the Christian element in Nicaea itself the seat of the metropolis was moved to the nearby port of Cius, whose local archbishopric was consequently abolished.

[6] The metropolis experienced a revival in late Ottoman times, as a result of the general demographic upswing of the Orthodox (not just Greek) population in this period.