About 13 kilometers north of the Azraq Junction, on the highway to Azraq, you will find the large black fortress of Qasr Al Azraq. The present form of the castle dates back to the beginning of the 13th century CE. Crafted from local black basalt rocks, the castle exploited Azraq's important strategic position and water sources.

The first fortress here is thought to have been built by the Romans around 300 CE, during the reign of Diocletian. The structure was also used by the Byzantines and Umayyads. Qasr Al Azraq underwent its final major stage of building in 1237 CE, when the Mamluks redesigned and fortified it. In the 16th century the Ottoman Turks stationed a garrison there, and Lawrence of Arabia made the fortress his desert headquarters during the winter of 1917, during the great Arab Revolt against the Ottoman Empire.

The castle is almost square, with 80-meter long walls encircling a central courtyard. In the middle of the courtyard is a small mosque that may be from Umayyad times, along with the main well. At each corner of the outer wall, there is an oblong tower. The primary entrance is a single massive hinged slab of granite, which leads to vestibule where one can see carved into the pavements the remains of a Roman board game. Above the entrance area is the chamber that was used by Lawrence during his stay in Qasr Al Azraq. The caretaker of the castle has a collection of photographs of Lawrence; in fact, his father was one of the Arab officers who served with the legendary Brit.

The copious springs in the oasis of Azraq made it an attractive place for settlement since the Lower Paleolithic Period. In the Roman period, the site was of crucial importance because of its location near the northern tip of Wadi Al-Sirhan, the natural migration route between southern Syria and the interior of the Arabian Peninsula.

A chain of fortresses defended the entrance to the Oasis; Aseikim, 15 km northeast of Azraq and Uwainid, another 15 km to the southwest, close to the Shaumari Nature Reserve.

An interesting feature of Azraq South is a large hexagonal reservoir built of dressed basalt stones and strengthened at regular intervals by rounded and triangular buttresses, placed against the outer and inner faces of the enclosing walls. These features bring to mind the large enclosures at Qasr Al-Hir East and Qasr Al-Hir West in Syria, which date to the Umayyad period.