The city walls of Diyarbakir are more than five kilometers long, among the longest of medieval fortifications; only the Great Wall of China is longer. It is constructed of imposing masonry in black basalt (a stone of local origin), and had along its circuit more than 75 towers, all but six of which are still standing. There are four original gates in the wall, the Harput gate in the north, the Yeni Kapi in the east, the Mardin gate to the south, and the Urfa gate to the west. The citadel of Diyarbakir is on a hill in the northeast corner of the wall, defended by its own ring wall built during the Ottoman period.

The location of the gates and the line of the wall dates from the late fourth century A.D. A north-south street connects the Mardin Gate with the Harput Gate; an east-west street connects the Urfa Gate with the Yeni Kapi. The central market is at the intersection of these main avenues. Although some Byzantine stonework is incorporated into the fortifications as we see them today, the late Roman walls were largely repaired or replaced piecemeal in Medieval times, in 909 by the Abbasid caliph Al Muktadir, and substantially during Diyarbakir's rise in prominence between the eleventh and thirteenth centuries.

Al Muktadir rebuilt the Harput gate and the Mardin gate following their intentional demolition by his predecessor ten years earlier. The Harput gate is a Byzantine design embellished during the rebuilding with crude animals carved in relief. The entrance, as are all gates, is heavily fortified between two half-round towers that project almost 15 meters from the line of the wall. The Mardin gate is similar in plan and decoration. Carved fauna became a tradition among subsequent rebuilders of Diyarbakir's towers and walls.

Sultan Malik Shah of the Great Seljuks built four towers on the western wall, celebrated in floriated Kufic inscriptions. One of these inscriptions, on a tower dated 1088, has a figural carving in the center of the dedication featuring a seated man flanked by two bulls, while at each end of the writing a lion is carved above a ram and an eagle with outstretched wings. Another similar tower, built in 1089, has carvings of a seated man with galloping horses at his sides above the inscription, and lions with knotted tails at each end of the first line. These are followed by hares facing each other and an eagle above a seated female nude.

In 1183 Diyarbakir became the capital city of the Artukids, who made the most significant additions to the walls. That year the Urfa Gate was rebuilt by the Muhammad, son of Kara Arslan. The gate has finely carved figures of dragons on either side of an inscription, and on the keystone of the arched gate is a bull's head surmounted by an eagle with outstretched wings. In the same area of the western wall, south of the gate, are the two most imposing towers, Ulu Beden and Yedi Kardes. Both were commissioned in 1208 by the Artukid al-Malik al-Salih Mahmud (who designed the Yedi Kardes tower himself). The Ulu Beden tower was built by the architect Ibrahim bin Jafar; Yedi Kardes was constructed by the architect Yahya bin Ibrahim Sufi. The Ulu Beden tower is almost a full circle in plan, as it defends a sharply acute angle in the walls. It is 25.5 meters in diameter, faced with smooth basalt, and encircled midway up its height by a monumental inscription. The bulk of the inscription is one line of Kufic script, but in the center there are three lines forming a rectangular focal point. Winged, human-headed lions decorate the top two corners of the plaque; the bottom corners are each decorated with bulls. In the center above the inscription is the Artukid double-headed eagle. The Yedi Kardes tower is similar in all respects to the Ulu Beden tower, but it is slightly larger, 27.8 meters in diameter.