The town of Iznik (ancient Nicaea) is unique in many respects: it hosted two ecumenical councils, and its location on the lake (tr. İznik Gölü) makes it an attractive holiday destination. However, the most unavoidable feature of Iznik are the well-preserved fortifications that still surround the city today. When entering Iznik, you must pass through one of the historical gates, and while walking around the city, you will notice the layout of communication routes preserved from ancient times. They are based on two main arteries crossing Iznik from east to west and from north to south.

The length of Iznik's fortifications is approximately 5 km, and there are four main gates leading to the city: İstanbul Kapısı, Yenişehir Kapısı, Lefke Kapısı, and Göl Kapısı. The remains of 12 smaller gates and 114 defensive towers have also been preserved. In some sections, the height of the walls reaches 13 meters.

The first defensive walls of Nicaea, mentioned by the Greek geographer Strabo, were built in the Hellenistic period, under the rule of Lysimachus, i.e. at the turn of the 4th and 3rd centuries BCE. Little of those fortifications has survived to this day. The defensive walls in Nicaea were then expanded in the shape of a pentagon surrounding the city at the end of the 1st century CE. during the reign of the Roman Flavian dynasty.

The earthquake of 123 CE seriously damaged the fortifications of Nicaea, as well as many other buildings of the city. Funds for the reconstruction were given to the city by Emperor Hadrian, to whom the eastern gate, i.e. Lefke Kapısı, was dedicated in gratitude.

In 268 CE, the city was captured and destroyed by the Goths. The fortifications were rebuilt on the orders of Emperor Claudius II, preserving their course from the 1st century AD. They have survived to this day in the appearance given to them then. Necessary repairs to the walls were carried out in Byzantine times. They were first renovated during the reign of Emperor Justinian, when they were again damaged by an earthquake. In the 7th century, the walls were strengthened during Arab invasions of Byzantium.

The least preserved of the main gates in Iznik is Göl Kapısı or the Lake Gate. Its remains are located on the western side of the city, near Lake Iznik.

The southern gate, called Yenişehir Kapısı, was built in the 3rd century CE. Its name is related to its location on the road leading from Iznik south to the city of Yenişehir. Between the Yenişehir Kapısı and Lefke Kapısı gates there is a well-preserved fragment of the defensive walls, which can be seen by following the path along them.

A Greek inscription on the eastern gate of Lefke Kapısı states that he built it in 123 CE. for Emperor Hadrian, proconsul Marcus Plancius Varus with the help of citizen Cassius Chrestos. The sarcophagus of Chrestos was found in the eastern necropolis and is exhibited in the garden of the Archaeological Museum in Iznik. The gate was expanded during the Byzantine period, when it was given a triple form. After reaching the top of this gate, you can see the surroundings of Iznik from an interesting perspective.

The northern gate (İstanbul Kapısı) was built in the times of Emperor Vespasian and renovated on Hadrian's orders. It is also a triple gate and is decorated with bas-reliefs and carved heads of Medusa.

On the section running west from this gate, there is the best-preserved fragment of Iznik's defensive walls, reaching a height of 11 to 13 meters. There are three towers with a square base, the walls of which are lined with white marble. The Istanbul Gate and its surroundings thus stand out from other fortifications in terms of colour. Perhaps it was a deliberate attempt to make an appropriate impression on guests coming from Constantinople.

Among the smaller gates, fragments of which can be seen in Iznik, it is worth mentioning the Palace Gate (Saray Kapısı) and the Rooster Gate (Horoz Kapısı). The name Saray Kapısı comes from the palace of Sultan Orhan, who lived in the 14th century, which was once located nearby.