The Tassili n'Ajjer is a sandstone plateau of southeastern Algeria, extending over seventy-two thousand square kilometres along the Libyan border between the Hoggar and the Erg Admer. Its name in Tamasheq means roughly "plateau of the rivers", a reference to the wadis that cut deep canyons across its surface.
The plateau preserves one of the densest concentrations of prehistoric rock art on earth: some fifteen thousand paintings and engravings span twelve thousand years of Saharan habitation, from the late hunter-gatherer Round Head period of the early Holocene through the cattle pastoralist period, when the Sahara was savannah, to the horse and camel periods that mark the desiccation of the region.
The art was systematically recorded for the first time by the French ethnologist Henri Lhote and his team between 1956 and 1962. The names given to individual painting sites by Lhote — the Great God of Sefar, the White Lady of Aouanrhet — have shaped subsequent interpretation, sometimes in misleading ways; recent scholarship has revised both chronology and reading.
The plateau was inscribed by UNESCO as a World Heritage Site in 1982 for cultural significance, and as a Biosphere Reserve in 1986 for the relict cypress and olive woodlands that survive in its higher canyons. The Kel Ajjer Tuareg, who give the plateau its name, are its traditional custodians.