Eight miles east of St Louis near Collinsville, Illinois are the Cahokia Mounds. Site of a prehistoric settlement of Mississippians who created the largest city in America at 20,000..eclipsed only by Philadelphia in 1800. The visitor center is very interesting and the hike around the grounds totally worth it.
https://cahokiamounds.org
The largest of the mounds (scroll down) is Monks. Monks Mound was constructed over a period of three hundred years by the natives using only baskets to carry up the soil. It covers 14 acres of ground - more than the great pyramid- and is 100 feet tall.
Monks mound above.
The next several shots are Monks Mound.
Above, the Skyline of St Louis from the top of the mound.
