[B]In another case, American archaeologistsRene Million and George Cowgill spent years systematically mapping the entirecity of Teotihuacan in the Valley of Mexico near what is now Mexico City. Atits peak around AD 600, this city was one of the largest human settlements inthe world. The researchers mapped not only the city’s vast and ornateceremonial areas, but also hundreds of simpler apartment complexes where commonpeople lived.