A vast desert of northern Africa extending east from the Atlantic coast to the Red Sea and south from the Atlas Mountains and the Mediterranean Sea to the Sahel. About 5,000 to 10,000 years ago, the Sahara was a region of savanna vegetation and extensive surface water, most of which had disappeared by Roman times. Introduction of the camel (probably in the first century AD) led to occupation by nomadic tribes who moved from oasis to oasis in search of water.