English: Qasr el-Azraq is of Roman origin, guarding the north of Wadi Sirhan, through which Bedouins found an inroad into the Roman-Byzantine province of Arabia. A first building phase dates from about 200 AD under Emperor Septimus Severus, a second from 300 AD, the time of Diocletian. Essentially that form remains, though in the 8th century it became a Umayyad castle. From the Ayyubid period dates the inscription above the entrance:, which mentions 1237. In the 16th century Turkish troops were housed here, until the soldiers were retreated to the Mecca-route.