11/16/1998 at 01:00 AM EST
The hunt began just after dawn one November morning last year. Filled with anticipation, British photographer David Coulson began climbing a slab of gray sandstone jutting out of the Sahara floor in the African nation of Niger. Fifty feet up, he found his quarry and stood amazed.
Etched in the stone were images of two giraffes, one 20 feet tall—perhaps the largest prehistoric rock art ever found. "We were stunned," says Coulson, 49, son of a former British ambassador to the U.S. "It was like entering an obscure art gallery and stumbling across a Renoir."
Unknown until now except to desert nomads, the extraordinary work was made 7,000 to 9,000 years ago by tribesmen who lived in the Sahara when it was less arid and giraffes were revered. But don't plan on trekking off to see the carving anytime soon. Coulson, who cofounded the Trust for African Rock Art in 1995, is keeping its location secret to protect it from vandals.