The large black fortress of Qasr al-Azraq is located about 13 kilometers north of the Azraq Junction, on the highway to Iraq. The castle has an important strategic position and access to water sources.
The present form of the castle dates back to the beginning of the 13th century AD, where it was built from local black basalt rocks. The first fortress is thought to have been built by the Romans around 300 AD. The structure was also used by the Byzantines and Umayyads. The Mamluks redesigned and fortified Qasr al-Azraq in 1237 AD, and in the 16th century the Ottoman stationed a garrison there. Later Lawrence of Arabia made it his desert headquarters, during the Great Arab Revolt against the Ottoman Empire in 1917.
The castle is almost square, with 80-meter long walls encircling a central courtyard, where a small mosque, that may be from Umayyad times, along with the main well were built. The primary gateway is a single massive hinged slab of granite. Above the entrance area is the room that was used by Lawrence during his stay there.