Qasr al-Azraq is a large fortress located in present-day eastern Jordan. It is one of the desert castles, located on the outskirts of present-day Azraq, roughly 100 km (62 mi) east of Amman. Its strategic value came from the nearby oasis, the only water source in a vast desert region. The name of the fortress and associated town came from these. The settlement was known in antiquity as Basie and the Romans were the first to make military use of the site, and later an early mosque was built in the middle.
It did not assume its present form until an extensive renovation and expansion by the Ayyubids in the 13th century, using locally quarried basalt which makes the castle darker than most other buildings in the area. Later, it would be used by the Ottoman armies during that empire's hegemony over the region. During the Arab Revolt, T.E. Lawrence based his operations here in 1917–18, an experience he wrote about in his book Seven Pillars of Wisdom. The connection to "Lawrence of Arabia" has been one of the castle's major draws for tourists.
The castle is constructed of the local black basalt and is a square structure with 80 metre long walls encircling a large central courtyard. In the middle of the courtyard is a small mosque that may date from Umayyad times. At each corner of the outer wall, there is an oblong tower. The main entrance is composed of a single massive hinged slab of granite, which leads to a vestibule where one can see carved into the pavement the remains of a Roman board game.
The strategic significance of the castle is that it lies in the middle of the Azraq oasis, the only permanent source of fresh water in approximately 12,000 square kilometres (4,600 sq mi) of desert. Several civilizations are known to have occupied the site for its strategic value in this remote and arid desert area.
The area was inhabited by the Nabataean people and around 200 CE fell under the control of the Romans. The Romans built a stone structure using the local basalt stone that formed a basis for later constructions on the site, a structure that was equally used by the Byzantine and Umayyad empires.
Qasr al-Azraq is often included on day trips from Amman to the desert castles, along with Qasr Kharana and Qasr Amra, both east of the capital and reached via Highway 40. Admission is JD 2. Visitors can explore most of the castle, both upstairs and downstairs, except for some sections closed off while the rock is shored up. There is little interpretive material at the moment.