Tassili n'Ajjer (Berber for "Plateau of the Rivers", in Arabic: طاسيلي ناجر) is a mountain range in the Sahara desert. It is a vast plateau in south-east Algeria at the borders of Libya, Niger and Mali, covering an area of 72,000 sq. km. The exceptional density of paintings and engravings, and the presence of many prehistoric vestiges, are remarkable testimonies to Prehistory. From 10,000 BC to the first centuries of our era, successive peoples left many archaeological remains, habitations, burial mounds and enclosures which have yielded abundant lithic and ceramic material. However, it is the rock art (engravings and paintings) that have made Tassili world famous as from 1933, the date of its discovery. 15,000 engravings have been identified to date.
It extends from 26°20′N 5°00′E east-south-east to 24°00′N 10°00′E, and the highest point is Adrar Afao, 2158 m, at 25°10′N 8°11′E. The nearest town is Djanet, about 10 km southwest of the range. Much of the range, including the cypresses and archaeological sites (see below), is protected in a National park, Biosphere Reserve and World Heritage Site, named the Tassili n'Ajjer National Park.
The property is also of great geological and aesthetic interest: the panorama of geological formations with "rock forests" of eroded sandstone resembles a strange lunar landscape.
The range is composed largely of sandstone. Erosion in the area has resulted in nearly 300 natural rock arches being formed, along with many other spectacular landforms.
Because of the altitude and the water-holding properties of the sandstone, the vegetation is somewhat richer than the surrounding desert; it includes a very scattered woodland of the endangered endemic species Saharan Cypress and Saharan Myrtle in the higher eastern half of the range.
The ecology of the Tassili n'Ajjer is more fully described in the article West Saharan montane xeric woodlands, the ecoregion to which this area belongs. The literal English translation of Tassili n'Ajjer is 'Plateau of the rivers' referring to a time when the climate was repeatedly far wetter than today (see Neolithic Subpluvial).
The range is also noted for its prehistoric rock paintings and other ancient archaeological sites, dating from neolithic times when the local climate was much moister, with savannah rather than desert. The art depicts herds of cattle, large wild animals including crocodiles, and human activities such as hunting and dancing. The art has strong stylistic links to the pre-Nguni Art of South Africa and the region, executed in caves by the San Peoples before the year 1200 BC.