Iznik is a town and an administrative district in the Province of Bursa, Turkey. The town lies in a fertile basin at the eastern end of Lake İznik, bounded by ranges of hills to the north and south. As the crow flies the town is only 90 km southeast of Istanbul but by road it is 200 km around the Gulf of Izmit. It is 80 km by road from Bursa.
The town is situated with its west wall rising from the lake itself, providing both protection from siege from that direction, as well as a source of supplies which would be difficult to cut off. The lake is large enough that it cannot be blockaded from the land easily, and the city was large enough to make any attempt to reach the harbour from shore-based siege weapons very difficult.
The city was surrounded on all sides by 5 km (3 mi) of walls about 10 m (33 ft) high. These were in turn surrounded by a double ditch on the land portions, and also include over 100 towers in various locations. Large gates on the three landbound sides of the walls provided the only entrance to the city.
Today the walls are pierced in many places for roads, but much of the early work survives and as a result it is a major tourist destination. The town has a population of about 15,000. It has been a district center of Bursa Province since 1930. It was in the district of Kocaeli between 1923–1927 and was a township of Yenişehir (bounded to Bilecik before 1926) district between 1927–1930.
The town was an important producer of highly decorated fritware vessels and tiles in the 16th and 17th centuries
