Diyarbakir Fortress and Castle The Diyarbakır Fortress, located in Sur, is a historical site consisting of an interior and exterior fortress. It comprises several structures, including a citadel atop a rocky hill that offers breathtaking views of the Tigris River. The fortress features four gates: Dağ (Mountain) Gate, Urfa Gate, Mardin Gate, and Yeni (New) Gate. The walls of the fortress were constructed in their current form in the mid-fourth century AD by Emperor Constantius II of the Roman Empire. The Diyarbakır walls are the second-largest complete defensive walls in the world, after the Great Wall of China. The fortress has been built, used, and rebuilt over the centuries during periods of Roman and Ottoman rule over the Diyarbakir region. The walls surrounding the metropolitan area measure up to 53 meters in height and contain 63 inscriptions from various historical periods, including Hurrian, Mede, Armenian, Roman, Sassanian, Byzantine Marwanids, Ayyubids, and Ottoman influences. The Diyarbakir Fortress dates back to 297 AD when it was initially built by the Romans. In 349 AD, Emperor Constantius II ordered the expansion of the walls to their current size. Over the course of its 1500-year history, the walls and towers have been reinforced with volcanic rock sourced from the surrounding region. The walls are adorned with 82 watchtowers, constructed primarily by the Romans and later restored by the Ottomans during the 15th and 16th centuries. When the Ottomans defeated the Safavids, they used cannons to destroy their walls, which had to be rebuilt. Today, the walls remain mostly intact, standing at about 33 feet in height and 10-16 feet in thickness. Although a section was demolished in the 1930s, the walls still encompass a circumference of 3 miles. In 2015, the Diyarbakir Fortress and Hevsel Gardens were recognized as a UNESCO World Heritage Site.