The Sahara ("desert" in Arabic) covers an area of over 8 million km2 from the Atlantic to the Red Sea, and marks the transition between Mediterranean North Africa (from Morocco to Egypt) and Black Africa. The image conjured up by the name Sahara is that of the desert's northern landscapes and the dunes of the Great Erg which make up the largest part of the Tunisian Sahara. However, the desert also comprises volcanic landscapes (Hoggar, Tibesti) and regs (huge expanses of rocks and stones). The best time to explore the Sahara is between September and May.