The research earned him a doctorate in Egyptology at Yale. He remembers “climbing all over the Sphinx like the Lilliputians on Gulliver, and mapping it stone by stone.” The result was a uniquely detailed picture of the statue’s worn, patched surface, which had been subjected to at least five major restoration efforts since 1,400 B.C. So Lehner settled in, working for five years out of a makeshift office between the Sphinx’s colossal paws, subsisting on Nescafé and cheese sandwiches while he examined every square inch of the structure. Little was known for certain about who erected it or when, what it represented and precisely how it related to the pharaonic monuments nearby. Fortunately for Lehner, it wasn’t just a metaphor that the Sphinx is a riddle. No human endeavor has been more associated with mystery than the huge, ancient lion that has a human head and is seemingly resting on the rocky plateau a stroll from the great pyramids. Working closely with a young Egyptian archaeologist named Zahi Hawass, Lehner also explored and mapped a passage in the Sphinx’s rump, concluding that treasure hunters likely had dug it after the statue was built.

They found only the cracks and fissures expected of ordinary limestone formations.

In 1977, he joined Stanford Research Institute scientists using state-of-the-art remote-sensing equipment to analyze the bedrock under the Sphinx. Lehner married an Egyptian woman and spent the ensuing years plying his drafting skills to win work mapping archaeological sites all over Egypt. “There were thousands of tombs of real people, statues of real people with real names, and none of them figured in the Cayce stories,” he says. Even as he grew skeptical about a lost hall of records, the site’s strange history exerted its pull. Still, he returned, finishing his undergraduate education at the American University of Cairo with support from Cayce’s foundation. “It was hot and dusty and not very majestic,” he remembers. When the foundation sponsored a group tour of the Giza plateau-the site of the Sphinx and the pyramids on the western outskirts of Cairo-Lehner tagged along. In 1971, Lehner, a bored sophomore at the University of North Dakota, wasn’t planning to search for lost civilizations, but he was “looking for something, a meaningful involvement.” He dropped out of school, began hitchhiking and ended up in Virginia Beach, where he sought out Cayce’s son, Hugh Lynn, the head of a holistic medicine and paranormal research foundation his father had started. During one of his trances, Cayce, who died in 1945, saw that refugees from the lost city of Atlantis buried their secrets in a hall of records under the Sphinx and that the hall would be discovered before the end of the 20th century. When Mark Lehner was a teenager in the late 1960s, his parents introduced him to the writings of the famed clairvoyant Edgar Cayce.

Secrets of great art