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The Sahara (Arabic: الصحراء الكبرى, aṣ-ṣaḥrā´ al-kubra, "The Greatest Desert") is the world's largest hot desert. At over 9,000,000 square kilometres (3,500,000 sq mi), it covers most of Northern Africa, making it almost as large as the United States or the continent of Europe. The desert stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. To the south, it is delimited by the Sahel: a belt of semi-arid tropical savanna that comprises the northern region of central and western Sub-Saharan Africa.
The Sahara has an intermittent history that may go back as much as 3 million years. Some of the sand dunes can reach 180 metres (600 ft) in height. The name comes from the Arabic word for desert: (صَحراء), "ṣaḥrā´" (ⓘ; [sˤɑħrɑːʔ]).