Cahokia

A thousand years ago, there was a city in Illinois that was bigger than London at the time. Cahokia had around 15,000 people, making it the biggest city in what later became the United States. It may have had large suburbs, too, because there were once plenty of manmade mounds across the Mississippi River that were bulldozed to build St. Louis. All that's left of Cahokia are the mounds, which are now protected and studied, and open to the public, too.

What led to the abandonment of Cahokia? It wasn't disease brought in by Europeans, as the city was declining 200 years before Columbus landed. It may have been crop failures due to drought, maybe it was war, or maybe its residents saw better opportunities elsewhere. PBS introduces us to what we know about the ancient city of Cahokia. (via via Damn Interesting)