“This place is a supernova,” said Mr. Schmidt, standing under a lone tree on a windswept hilltop 35 miles north of the Syrian border.

“Within a minute of first seeing it, I knew I had two choices: go away and tell nobody, or spend the rest of my life working here.”

Behind him are the first folds of the Anatolian Plateau. Ahead, the Mesopotamian plain, like a dust-colored sea, stretches south hundreds of miles to Baghdad and beyond. The stone circles of Gobekli Tepe, his workplace since 1994, are just in front, hidden under the brow of the hill.

Compared with Stonehenge, they are humble affairs. None of the circles that have been excavated, four out of an estimated 20, is more than 100 feet across. Two of the slender, T-shaped pillars tower at least three feet above their peers.

What makes them remarkable are the carved reliefs of boars, foxes, lions, birds, snakes and scorpions that cover them, and their age. Dated at about 9500 B.C., these stones are 5,500 years older than the first cities of Mesopotamia and 7,000 years older than Stonehenge.