Grand Erg Oriental follow the wind's direction. There are other types of dunes, as well as "complex" dunes. Saharan winds are also known to clear an area of sand altogether, leaving bare rock (hamada) or gravel (reg). The "Grand Erg Oriental" is accessible overland by an Algerian road, which goes south from Constantine. It passes through the Aurès mountains, then salt lakes by the city of Biskra. Next the road skirts the western edge of the erg. After about 500 km. in all, it reaches the ancient oasis of Ourgla [Wargla]. Since late antiquity Wargla was a stop for the Saharan trade, being
Erg of Bilma Erg of Bilma The Erg of Bilma is a dune sea (Arabic: "erg") in the Ténéré desert region of the south central Sahara Desert. The Erg of Bilma stretches southwest from Fachi and the Tibesti Mountains. On the west it is bounded by the Aïr Mountains in north central Niger, and to the east it passes Bilma, continuing on to the Chadian border. It surrounds on three sides the oasis of Bilma, southernmost of a north–south string of oasies of the Kaouar rise. The Erg covers an area of approximately . At its southernmost edge, some of the dunes have