It was massive, one of the first great cities of the Western Hemisphere. And its origins are a mystery.

It was built by hand more than a thousand years before the swooping arrival of the Nahuatl-speaking Aztec in central Mexico. But it was the Aztec, descending on the abandoned site, no doubt falling awestruck by what they saw, who gave its current name: Teotihuacan.

A famed archaeological site located fewer than 30 miles (50 kilometers) from Mexico City, Teotihuacan reached its zenith between 100 B.C. and A.D. 650. It covered 8 square miles (21 square kilometers) and supported a population of a hundred thousand, according to George Cowgill, an archaeologist at Arizona State University and a