Back in January when I visited St. Louis, one of the places I stopped was Cahokia. It's located a couple of miles up the road and river from St. Louis in Illinois, on the banks of an oxbow lake.
It was the largest native settlement north of Mexico and its heyday was about 1100-1300 CE, roughly the same time as the High Middle Ages in Europe. After that, people just left.
They built large earthen platforms and mounds, basketful by basketful of dirt over the course of a few centuries.
It was very winter, yet we persevered all the way to the summit, an increase in elevation of over 28,000 millimeters.
The city was in the flat land between the mounds. The exhibits in the visitor center talked about how the remnants of a palisade have been found encircling the site. That's interesting because that means that they had enough resources to support a city and city dwellers in the first place and then enough economy to defend it and then for there to be enemies with weapons. Or maybe who ever controlled the city wanted only a few entryways, perhaps for tax purposes.
From the top of the mound they could definitely see the surrounding land. In modern times the skyline of St. Louis is on the horizon.