Scant foundations remain of the church that was once famous as the burial place of the Byzantine emperor Theodore I (Lascaris). Built around 800 and reconstructed after a mid-11th century earthquake, it is the only church in İznik that was never converted into a mosque; unsurprisingly, it was dynamited by victorious Turks after the War of Independence.

Lascaris, who established the Empire of Nicaea after the Crusaders' 1204 conquest, built the city's outer walls, which were then supported by more than 100 towers and protected by a wide moat.