archaeologist dolph widmer has studied teotihuacan for more than a decade. amazing things about teotihuacan is that it's a city. and even though right now it's an agricultural field -- you see cactus everywhere -- you can still tell it's a city because the surface of the ground is littered with artifacts. they're everywhere. we can see that we have a site. here i have cultural material, like this piece of obsidian. i have a piece of ceramics. all this stuff here tells me that people lived here. and by noting the artifacts on the surface, i can get an idea how big their residences were, how many residents there were in the city, as a whole, and get some idea of the size and number of people that lived here. keach: during the 1960s, archaeologists surveyed the entire city, revealing an urban grid as deliberate as the streets of manhattan. a total of 2,600 buildings lined densely packed streets. 80% of these were residential compounds. these compounds enclosed numerous sleeping rooms, patios and kitchens. archaeologists estimate that 30 to 100 people could be h