Iznik is a completely "open air museum" with its rare ancient history and uniqueness. Historical urban fabric is preserved with its Hellenistic era grid-planned urban settlements and monumental buildings from Roman, Byzantine and Ottoman period. İznik, which is located 86 km northeast of Bursa, is established on the eastern shore of the lake known by the same name. Iznik settled between olive groves, vineyards and orchards and it is surrounded by two thousand years walls that are approximately 5 km in length. The traces of civilization dated back to 2,500 BC are hidden at Cicekli, Karadin and Cakırca mounds close to the city. The established settlements was named as ‘Helikore’ before the migration of Thracian tribes in the 7th century BC Khryseapolis (Gold City) name is read on the printed coins.
The city is renovated by Macedonian emperor Alexander's general Antigonus in BC 316 years and the city is referred as Antigoneia. After the death of Alexander, the battle between Antigonus and the generals Lysimakhos is resulted with Lysimakhos’victory and he named the city after his wife Nicaea – the daughter of Antipatros. The city was decorated with important architectural buildings and centralized to Kingdom of Bithynia at BC 293. Nicaea remained as the capital of the Kingdom of Bithynia for a while and continued to be an important residential area of Rome. When the Roman Empire is divided into two governance areas starting from A.C. 285 as East Rome and West Rome, Nicaea remained in the Byzantine Eastern Roman Empire borders. Nicaea sees great development in the hands of the Byzantines. Churches, waterways and cisterns are made in the city during this period.
The Turks entered the Byzantine interior after Seljuk Sultan Alpaslan at Malazgirt in 1071 defeated the Byzantine army. Kutalmışoğlu Suleyman Shah took over Nicaea in 1075 and made it the capital of the Seljuk state. The city walls were re-made and change the name of the city as Iznik which means 'the trace of Nicaea”. Thus Iznik became the first Turkish capital of Anatolia. The second Byzantine period began in Iznik when 1. Kılıcarslan could not hold in the front of the Crusaders and fled the city (1096). During this period, major repairs were undertaken on the city walls and a front wall (front walls) were built to enhance the city strength. When Osman Ghazi, who made Yenisehir as center in 1299, sieged Iznik Byzantine emperor sent forces. Osman Ghazi earned a victory in Yalova on July 27, 1302 and accelerated the foundation of Ottoman Principality. Iznik, Orhan Bey was conquered by Orhan Bey (1326-1362) in 1331 and re-entered under the Turkish administration. Iznik became an important art, trade and cultural center. The city was developed entirely by building many mosques, madrasas, khans and baths with close attention of Sultan II. Murad and Grand Vizier Candarli family. Iznik was transformed into a cultural center where many scholars and poets educated in 14th and 16th century. The most famous scholars of the era began teaching in the madrassas of Iznik, therefore Iznik is also called as "Ulema's Nest" (Land of Scholars).
The first madrasa and hospice of the Ottoman period were built in İznik. Iznik is occupied by Greek forces after signing the Armistice of Montrose as a result of the defeat of Ottoman Empire 1. N World War 1. The first occupation, which continued for 2 months and 18 days, as broken as a result of the resistance launched with the participation of local people on September 30, 1920. However, the city was once more occupied on November 24, 1920 and liberated again on 27-28 November 1920. Mustafa Kemal Pasha's victory brings on August 30, 1922 brought the definitive liberation. Today, Iznik which has the most important cultural heritage in the world is poised to become one of the important faith tourist centers.
The third holy city of Christendom:
Nicaea is also one of the most important religious center of the Christian world. The first council, in which the main principles of the Christianity is determined, was gathered at the Palace of Senatus in Nicaea at 325 AD with the participation of 228 bishops. Emperor I. Constantine was attended to the meeting and two important aspects were discussed. According to Alexandrian reverend Arius ''Jesus is only a man, and he didn’t come into the world as the son of God ". The bishops opposed to this thesis which gained supporters in a short time. "Jesus is the Son of God” thesis, which is the case believed in Christian world today, accepted after long discussions. 20-point text about Christianity which is known as the ferial days and the law of Nicaea, was accepted after this council. Because of this İznik was declared the third holiest city after Jerusalem and Vatican City in 1962 with 19th council. In addition, 7th Council gathered at the Nicaea Hagia Sophia in the year 787 and the bans on picture and the statue removed were removed under the leadership of Empress Irene.