arid wasteland of southwestern Asia, extending northward from the Arabian Peninsula over much of northern Saudi Arabia, eastern Jordan, southern Syria, and western Iraq. Receiving on the average less than 5 inches (125 mm) of rainfall annually and largely covered by lava flows, it formed a nearly impenetrable barrier between the populated areas of the Levant and Mesopotamia until modern times; several major motor routes and oil pipelines now bisect it. In the late 1970s, there was much oil exploration. The desert, the southern sector of which is commonly known as Al-Ḥammād, is inhabited by several nomadic tribes and breeders of Arabian horses.