Somewhere not far from Cahokia Mounds Historic Site there is a landfill. You could see it from the interstate and from the top of Monk’s Mound, the largest earthen mound at Cahokia. Monk’s Mound is 100 feet tall. Monk’s Mound was easily the tallest man-made thing in North America when it was built hundreds of years ago. The landfill— merely one pile of refuse from one middling city in a vastly more advanced civilization— dwarfs Monk’s Mound.
The exhibits at Cahokia emphasize the (relative) sophistication of the city. Which is true, for North America of the time, but in the big picture Cahokia was a good seven thousand years behind Old World civilizations. The Cahokians built and maintained their city and trade network without: the wheel, metal tools, masonry, draft animals, a system of writing, or currency. The causes of Cahokia’s decline and demise are not known, only that they were gradual and not catastrophic, but I’m not too terribly surprised that Cahokia declined and vanished. I’m more impressed that it lasted as long as it did.