I think the ancient city of Cahokia has largely gone unconsidered, when compared to the large stone edifices built in the south of Mexico, in Central America, and in the northern reaches of South America. But it was impressive and large in contrast to just about anything around (though there were some large communities with mounds down along the southern Mississippi River also).

What Doomed the Great City of Cahokia? Not Ecological Hubris, Study Says

Excavations at the city, famous for its pre-Columbian mounds, challenge the idea that residents destroyed the city through wood clearing.

A thousand years ago, a city rose on the banks of the Mississippi River, near what eventually became the city of St. Louis. Sprawling over miles of rich farms, public plazas and earthen mounds, the city — known today as Cahokia — was a thriving hub of immigrants, lavish feasting and religious ceremony. At its peak in the 1100s, Cahokia housed 20,000 people, greater than contemporaneous Paris.

By 1350, Cahokia had largely been abandoned, and why people left the city is one of the greatest mysteries of North American archaeology.

Now, some scientists are arguing that one popular explanation — Cahokia had committed ecocide by destroying its environment, and thus destroyed itself — can be rejected out of hand. Recent excavations at Cahokia led by Caitlin Rankin, an archaeologist at the University of Illinois at Urbana-Champaign, show that there is no evidence at the site of human-caused erosion or flooding in the city.

The story is a lot longer, find the rest at the link.

There isn't a lot to be seen from above on Google Earth but if you search Cahokia Mounds State Historic Site you'll see a 360^o photo from the tallest mound.