The Mound Builders of Eastern North America

Most Americans are unaware that an American Indian civilization in our Great Plains built one of the largest pyramids anywhere in the world. We all know about the pyramids of Egypt and many of us are aware of the pyramids in Central America, but how many of us have ever even heard about Monk's Mound just outside St. Louis, Missouri? Monk's Mound was a ceremonial temple in the center of a once huge city, called Cahokia .

Cahokia was home to some tens of thousands of inhabitants. It was an important trading and religious center during its peak between 1050 and 1250 AD. Its artisans produced splendid copper ornaments, fine ceramics, and carved statues. Their structures were built of earth, rather than stone, and included defensive structures, sacred enclosures, altars, burial mounds, and temples. Monk's Mound (see the picture below), consisting of four platforms, was the most imposing structure in Cahokia and consisted of 22 million cubic feet of earth. The tallest of its four platforms was 100 feet high. Today, some 70 of the 120 original mounds in Cahokia survive and are maintained by our state park system.

Monks Mound Today

To sustain themselves, the Indians of Cahokia and the surrounding towns depended mainly on growing maize (corn) for food and the hunting of buffalo and antelope. For some 700 years, the Mississippian culture dominated the central and lower Mississippi, lower Ohio and Red River Valleys. At its height, there were hundreds of major towns and thousands of smaller settlements. Cahokia, a complex that covered nearly six square miles, was the largest. To feed such a population required an intensive, well-developed and organized system of agriculture. Yet, sometime around 1250 or 1300 AD, this civilization began to decline.

As with Mycenae, a change in the jet stream may have been the reason why. About 800 years ago, the jet stream changed course and moved further south than usual, bringing a 200-year drought to the northern Great Plains. July is the critical month for rain in that region. Today, the northern Great Plains receives about 25 inches of rain a year and produces good crops of maize and soybean. A drop in rainfall can profoundly affect the final crop yields, and slight shifts in the jet stream can result in rainfalls 25 percent or more below normal. Archaeologists, examining Mississippian sites in Iowa report a significant change in vegetation around 1200 AD to more drought tolerant species and a corresponding decrease in corn production.

Further south in Nebraska, where the jet stream was then passing, the July rainfall was unusually heavy, and the Indian population in this area began to increase. I wonder why? Could it be rainfall for crops… say corn?

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