The Ayasofya (St. Sophia) Cathedral was the seat of the first ecumenical council of 325 and the seventh council of 787.

Ayasofya Museum (İznik / Nicaea)
The Church that turned Politics into a mosque
Other things to do
The Ayasofya (St. Sophia) Cathedral was the seat of the first ecumenical council of 325 and the seventh council of 787.