Sometime between 9,000 and 7,000 years ago, African artisans carved this remarkable giraffe on a high wall of sandstone in the Sahara Desert of northeastern Niger. The giraffe, one of two large giraffe carvings on the same outcrop, stands a remarkable 20 feet tall--and is probably the largest known prehistoric engraving, says documentary photographer David Coulson of the Trust for African Rock Art, who reported its existence last year. Other, cruder images surrounding the giraffes were likely incised much more recently. Nothing, Coulson says, is known about the people who carved the animals (except that they didn't live in a desert; at the time the engravings were made, the Sahara enjoyed a much more temperate climate than today). "One of the things about the Sahara is that there have been so many peoples and cultures and civilizations that have come and then just vanished into the sands, largely because of the very extreme climatic shifts that have taken place over the millennia," Coulson says. "But we know incredibly little about any of them."