İznik, historically known as Nicaea, 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 of walls about 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.
For the history before the Ottoman conquest see: Nicaea.
In 1331, Orhan I captured Iznik from the Byzantines and for a short period the town became the capital of the expanding Ottoman emirate. The large church of Hagia Sophia in the centre of the town was converted into a mosque and became known as the Orhan Mosque. A madrasa and baths were built nearby. In 1334 Orhan built a mosque and an imaret (soup kitchen) just outside the Yenisehir gate (Yenişeh Kapısı) on the south side of the town.
The Arab traveller, Ibn Battuta, stayed in Iznik at the end of 1331 soon after the capture of the town by Orhan. According to Ibn Battuta, the town was in ruins and only inhabited by a small number of people who were in the service of the sultan. Within the city walls were gardens and cultivated plots with each house surrounded by an orchard. The town produced fruit, walnuts, chestnuts and large sweet grapes.
A census in 1520 recorded 379 Muslim and 23 Christian households while a census taken a century later in 1624 recorded 351 Muslim and 10 Christian households. Assuming five members for each household, these figures suggest that the population was around 2,000. Various estimates in the 18th and 19th centuries give similar numbers. The town was poor and the population small even when the ceramic production was at its peak during the second half of the 16th century.
The Byzantine city is estimated to have had a population of 20–30,000 but in the Ottoman period the town was never prosperous and occupied only a small fraction of the walled area. A succession of visitors described the town in unflattering terms. After his visit in 1779 the Italian archaeologist Domenico Sestini wrote that Iznik was nothing but an abandoned town with no life, no noise and no movement. In 1797 James Dallaway described Iznik as "a wretched village of long lanes and mud walls...".