Tassili n'Ajjer

Tassili n'Ajjer is a 72,000-square-kilometre sandstone plateau in south-eastern Algeria, eroded over millions of years into a labyrinth of rock formations, canyons, and natural arches. Since its rock art was first documented for Western science in the 1930s and systematically catalogued by French archaeologist Henri Lhote from 1956, the plateau has been found to contain more than 15,000 individual paintings and engravings, ranging in age from roughly 12,000 years ago to the early centuries CE, depicting a vivid record of the Sahara's transformation from a fertile savanna teeming with elephants, hippopotamuses, and crocodiles into the desert it is today, alongside scenes of cattle herding, hunting, and ritual dance. The site became Algeria's first UNESCO World Heritage Site in 1982.

Among the most famous images is a roughly 6-metre-tall painted figure known as the "Great God" or "Great Martian God" of Sefar, a round-headed humanoid form that French archaeologist Henri Lhote himself, in his popular 1958 account of the discoveries, suggestively compared to a figure in a "diving suit" or helmet — a comparison that, stripped of Lhote's original archaeological context, was later seized upon by ancient-astronaut writers including Erich von Däniken as evidence of prehistoric contact with extraterrestrials. Mainstream archaeologists regard the figure as belonging to the so-called "Round Head" period of Saharan rock art (roughly 10,000–8,000 years ago) and interpret the rounded forms as stylised depictions of ritual masks or shamanic figures, consistent with similar imagery found across other Round Head sites in the central Sahara.