Antigonos, who was a commander in Alexander the Great’s army and who had founded the city called "Antigoniea," died in 316 B.C. whereas the city passed over into the control of another commander called Lysimachos. Lysimachos developed and beautified the city which he renamed after his wife Nikaea. Following the death of Lysimachos in 293 B.C., the city was taken over by the Bthynians.

The Romans took control of the city in the 2nd century B.C. and later on it was ruled by the Byzantines. It is known that the first Christianity Council was held here in the year 325 A.D. In 1080, the Seljuk Sultan Kutalmisoglu Suleyman Sah captured the city and made it the Seljuk capital, but the Byzantines regained the city in 1097. In 1204, the Byzantines fled here during the Latin plunder of Constantinople whereas it remained their capital for 57 years. Orhan Gazi made the city a part of Ottoman territory in 1330 whereas the name was changed to its current name of Iznik. The designs found on the walls surrounding the city, which date from the Roman Period, were an important source of inspiration in the art of Ottoman ceramics. Traces of some structures that once ornated ancient Iznik can be found today. In the southern part of the city, one can see remains of a theater that was constructed in the Traian period. A three-columned basilica known as the Iznik Hagia Sofia can be seen in the middle of the city. The Turks turned it into a mosque and later the famous architect Sinan had some additional structures built around it. Besides this, there is an obelisk that was formed from five blocks of stone, a grave chamber constructed in the 4th century B.C. along with some foundations and marble flooring, which are all that remains from the 9th century Koimesis Church.

The Haci Ozbek Mosque with its single dome represented Iznik’s Turkish Period masterpieces and was considered to be a pioneering effort in the development of Ottoman mosques. The Yesil (Green) Mosque, which was built between 1378-91, is regarded as the most important mosque in Iznik in which Candarli Halil Pasha commissioned Architect Haci Musa to complete the work. The Nilufer Hatun Hospice was constructed next to the Green Mosque in 1388 and was named after the mother of Sultan Murat I, Nilufer Hatun. Today, it is used as a museum. In addition, some of Iznik’s historical mosques are the Orhan Gazi Mosque, built in 1334, the Mahmut Celebi Mosque, built in 1442, the Seyh Kubbeddin Mosque, which dates from the beginning of the 15th century, the Suleyman Pasha Complex, which dates back to the 14th century and the Yakup Celebi Mosque, which was commissioned by the son of Murat I, Yakup Celebi, in the year 1380.

The fabulous Iznik tiles that were created in workshops along Lake Iznik in the 15-17th centuries were used in the structures of that age and earned the amazement of the entire world. Today masterpieces originating from Iznik, such as the porcelain tiles that decorate numerous mosques, tombs, palaces and villas along with porcelain plates and oil lamps are on display in museums in Turkey and throughout the world.