Monks Mound, Cahokia Illinois, the largest Native American earthwork prior to the arrival of Columbus (rbw)

Many Americans lack a sense of history regarding their surroundings. It is often assumed that American history began with the Jamestown colony, but this is largely due to a systematic attempt during the early 20th century to forget the past. In fact, some of the evidence to the contrary can be found in the burial and effigy mounds that dot the American landscape. Thousands of mounds can be found, especially in the Mississippi, Missouri, and Ohio River systems. The Moundbuilders built these mounds for a large variety of purposes, but did so over a very long period of North American history. The largest mound, Monk’s Mound, was once near the center of a city, Cahokia, with a population of around 20,000 at its height around 1,000 C.E. It is located a few miles north of the intersection of the Ohio and Mississippi Rivers. Modern society could be informed by learning more about its history: Changes to the local climate and environmental degradation (such as deforestation) created an upheaval to Native American cultures by the 13th century C.E. This led to the consequence that subsequent cultures lived in smaller, more widely scattered bands by the time Europeans arrived.

Wikipedia: Mound Builders