Nicaea is an ancient and medieval city on the site of the modern Turkish city of Iznik. The city is located on the shore of the lake, and from the land it is limited by high hills, which created the best conditions for the defense of the city during the siege. Walls about 10 m high, a deep ditch dug in front of the wall and about 100 fortress towers provided reliable defense. The most difficult and controversial stage in the history of Nicaea, as well as throughout Asia Minor, fell on the 11th-15th centuries, when the region went through a painful transformation from Greek to Turkish, and most of the inhabitants completely changed their language, religion and identity. Until 1922, the Assumption Church, decorated with mosaics, remained the most significant monument of Byzantine art in Asia Minor. In 1922, it was destroyed by the Turkish authorities.
The ancient walls with towers and gates are relatively well preserved. The thickness of the walls is from 5 to 7 m, the height is from 10 to 13 m. The walls are made of large slabs of the Roman period and square stones, fastened with cement. The city could be entered through 4 large and 2 small gates. In some places you can see columns, other architectural fragments, the remains of ancient buildings. The walls of Nicaea resemble those of Constantinople built in the 4th century BC. n. e. On some towers you can see Greek inscriptions. Inside the Greek fortifications are the ruins of mosques, baths, Greek temples and churches, and other buildings. Outside the city walls, the remains of an aqueduct are visible.