Rub' al-Khali, Desert,Saudi Arabia:

The Rub' al Khali   is the largest sand desert in the world, encompassing most of the southern third of the Arabian Peninsula, including Saudi Arabia and areas of Oman, the United Arab Emirates, and Yemen. The desert covers some 650,000 square kilometres (250,000 sq mi) (the area between long. 44°30′ −56°30′E., and lat. 16°30′ −23°00′N).Desertification has increased through the millennia. Before desertification made the caravan trails leading across the Rub' al Khali so difficult, the caravans of the frankincense trade crossed now virtually impassable stretches of wasteland, until about AD 300. It has been suggested that Ubar, or Iram, a lost city, depended on such trade. The traces of camel tracks, unidentifable on the ground, appear in satellite images. More recently, tribal populations were also present in certain parts of the Empty Quarter, with the largest in the Najran region. A few road links were connected with these tribal settlements to the water resource and oil production centers.

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