a population center in northwestern Turkey, in the vilayet of Bursa, near the eastern shore of Lake İznik. Population, approximately 8,000.

The city was founded in the fourth century B.C. by the Macedonian king Antigonus I (reigned 306–301 B.C.) and was given the name Antigonia. The diadochos Lysimachus changed the city’s name to Nicaea (Greek, Nikaia). During the first century B.C. it came under Roman rule. From the end of the fourth century A.D. to the beginning of the 13th century the city was the most important trading, crafts, and cultural center of Byzantium. Ecumenical councils were held in Nicaea in 325 and 787. During the Arab-Byzantine wars of the seventh through tenth centuries the city was besieged twice by the Arabs, but they were unsuccessful. In 1081 it was captured by the Seljuks, and until 1097 it was the capital of the Seljuk Sultanate of Rum. In 1097, during the First Crusade, the city was returned to Byzantium. During the period 1204–61 it was the capital of the Nicaean Empire. In the 14th century it was conquered by the Ottoman Turks (since that time it has been called İznik) and became the first residence of the sultan Orkhan (reigned 1324–59/60 or 1362). İznik began to decline in the middle of the 17th century, and by the middle of the 18th century its population had decreased from 10,000 to 1, 500.

Remnants of Hellenistic structures have been preserved (parts of the theater and the city walls with sections reconstructed during the medieval period). Among the well-known Byzantine structures are the churches of the Assumption (seventh and tenth centuries, mosaics from the seventh through ninth and 11th centuries; church is nonextant) and St. Sophia (eighth century, with murals from the 13th century). Among the Turkish monuments are mosques (Yeşil Cami, or the “Green Mosque,” 1379–93; Kutbeddin Pasha, 14th century), the imaret Nilüfer Hatun (1389), the madrasa of Suleiman Pasha (1336 [?]), and the mausoleum of Hayreddin Pasha (1379).