As a child, Klaus Schmidt used to grub around in caves in his native Germany in the hope of finding prehistoric paintings. Thirty years later, as a member of the German Archaeological Institute, he found something infinitely more important: a temple complex almost twice as old as anything comparable.

"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.