High on a plateau in central Mexico lies the remains of a city that keeps to perplex archaeologists and historians. Of the many ancient cities of the Americas, Teotihuacan is among the most enigmatical. No one knows what race of people created it, what they used it for, or why it was abandoned. Without a doubt, the remains are awe-inspiring, but it is believed that 90 percent of this city is still buried under the arid Mexican soil. And yet, this an amazing city of culture held 200,000 residents at its peak. So what happened at Teotihaucán?