The Bursa Castle: The Bursa Castle is existing since the beginning of the 1st century B.C. Today the city walls are about 2 km long. There are two towers between Çakırhamam and Tophane, one of them round the other square. On the road leading to Tophane is the Castle Gate. There is a natural wall at the site of Topane, Tümen and the Art Institute all the way to Yıldız Kahve, in front of which is the Thermal Gate (Kaplıca). The wall continues from there to the Dungeon Gate (Zindan). There are the remains of a prison here on either side of the wall. The best-preserved section of the wall is from this gate to Üftade. On the flat area from Pınarbaşı to Cilimboz brook, there is a double wall. In front of Pınarbaşı is the fourth city gate, the Spring Gate (Pınarbaşı). The fifth gate, the Yer Gate, is at Üftade. The cave found under the walls is 79 m long, 5 m wide and 4 m high.
The Yer Kapı: This gate is one of the city gates of Bursa and is located beside the Üftade Mosque.
The İznik Castle: The castle dates back to 258 B.C. There are 4 gates in the castle: İstanbul, Yenişehir, Lefke and Göl, respectively. In addition to these, there are 12 secondary entrances. To strengthen the 4970 m long and the 10-13 m tall walls, the 114 towers were built along them. The old towers are round while the newer ones are square. There are also another 131 towers along the defensive line in front of the castle walls. The walls of Iznik have been often repaired with much of the rubble from the old city being used for this task. In the Byzantine era, in the strengthening of the walls against the Arab invaders a variety of materials were used. The reliefs on the Istanbul and Lefke Gates depict a battle of the 3rd century B.C.
The Lefke Gate: İznik's eastern gate, it was built for Hadrian in the 2nd century. The gate is actually composed of 3 gates within one another.
The İstanbul Gate: Built during the reign of the Roman emperor Vespasianus in the 3rd century A.D., it has 3 gates side by side.
The Yenişehir Gate: This is the city's southern gate. It was built between 270-288 A.D. during the reign of Claudius. Today the majority of the monument is in ruins.