Rock Painting at Tassili, AlgeriaThis scene of cattle grazing while a man stands guard over them was found on a rock face in Tassili n’Ajjer, a mountainous region in the Sahara where over fifteen thousand of these paintings have been catalogued. The oldest date back 9,000–12,000 years. Behind the man are perhaps his two children at play and his two wives working together in the compound. A cow stands in the enclosure to the right. (George Holton/Photo Researchers, Inc. Colorization by Robin Treadwell)