Colorado researchers have discovered and partially mapped a major urban center once occupied by the Purépecha of Mexico, a little-known people who fought the Aztecs to a standstill and who controlled much of western Mexico until diseases brought by the Spanish decimated them.

The "proto-urban center," which researchers have not yet named, sat on volcanic rock on the shores of Lake Pátzcuaro in the central Mexican state of Michoacan, now a tourist destination. It supported as many as 40,000 people until the consolidation of the Purépecha empire about AD 1350 led most of its inhabitants to relocate to the new capital of Tzintzuntzan, six miles away.

Finding that the urban center's population fell as the capital, Tzintzuntzan, grew will also help rewrite the history of the Purépecha, who were also known as Tarascans, said archaeologist Gary Feinman of Chicago's Field Museum, who was not involved in the research.