The siege of Nicaea by the forces of Orhan I from 1328 to 1331, resulted in the conquest of a key Byzantine Greek city by the Ottoman Turks.

When it was clear that no effective Imperial force would be able to restore the frontier and drive off the Ottomans, the city proper fell on 2 March 1331.

[5] The inhabitants of Nicaea were quickly and willingly incorporated into the growing Ottoman Empire, and many of them had already embraced Islam by 1340.

[6] Patriarch John XIV of Constantinople wrote a message to the people of Nicea shortly after the city was seized.

His letter says that "The invaders endeavored to impose their impure religion on the populace, at all costs, intending to make the inhabitants followers of Muhammad".

The Patriarch advised the Christians to "be steadfast in your religion" and not to forget that the "Agarians [Turks] are masters of your bodies only, but not of your souls."