A gate at the east side, not to be confused with a similarly named area in Istanbul. From the web:
The New Gate to the east of the walls is a single-entry gate with a flat arch, built in the Byzantine period in 1240-1241. The New Gate, or with its other known names, the Tigris or Water Gate, is one of the four gates of the Diyarbakır city walls. [...] It has a flat arch and a single entrance, and connects the city to the Tigris River. Despite the repairs it has undergone, it has preserved its character as a Byzantine-era structure. In an inscription in the Diyarbakır Ulu Mosque, the New Gate is referred to as the Water Gate.