Cahokia Mounds in the context of "Smithsonian trinomial"

Madison County is located in the U.S. state of Illinois. It is a part of the Metro East in southern Illinois. According to the 2020 census, it had a population of 264,776, making it the eighth-most populous county in Illinois and the most populous in the southern portion of the state. The county seat is Edwardsville, and the largest city is Granite City.

Madison County is part of the Metro East region of Greater St. Louis. The pre-Columbian city of Cahokia Mounds, a World Heritage Site, was located near Collinsville. Edwardsville is home to Southern Illinois University Edwardsville. To the north, Alton is known for its abolitionist and American Civil War-era history. It is also the home of the Southern Illinois University School of Dental Medicine. Godfrey, the village named for Captain Benjamin Godfrey, offers Lewis and Clark Community College formerly the Monticello Female Seminary.

Cahokia is a settlement and former village in St. Clair County, Illinois, United States, founded as a colonial French mission in 1689. Cahokia is on the east side of the Mississippi River in the Greater St. Louis metropolitan area. As of the 2010 census, it had a population of 15,241. On May 6, 2021, the village was incorporated into the new city of Cahokia Heights.

The name refers to one of the clans of the historic Illiniwek confederacy, who met early French explorers to the region. Early European settlers named the nearby (and long-abandoned) Cahokia Mounds in present-day Madison County after the Illini clan. The UNESCO World Heritage Site and State Historic Park were developed by the Mississippian culture, active here from 900 to 1500 AD. A connection to the clan is possible but unknown. The area was part of an extensive urban complex, the largest of the far-flung Mississippian culture territory through the Mississippi and Ohio River Valleys.

Monks Mound is the largest Pre-Columbian earthwork in the Americas and the largest pyramid north of Mesoamerica. The beginning of its construction dates from 900 to 955 CE. Located at the Cahokia Mounds UNESCO World Heritage Site near Collinsville, Illinois, the mound size was calculated in 1988 as about 100 feet (30 m) high, 955 feet (291 m) long including the access ramp at the southern end, and 775 feet (236 m) wide. This makes Monks Mound roughly the same size at its base as the Great Pyramid of Giza (13.1 acres / 5.3 hectares). The perimeter of its base is larger than the Pyramid of the Sun at Teotihuacan. As a platform mound, the earthwork supported a wooden structure on the summit.

Unlike Egyptian pyramids which were built of stone, the platform mound was constructed almost entirely of layers of basket-transported soil and clay. Because of this construction and its flattened top, over the years, it has retained rainwater within the structure. This has caused slumping, the avalanche-like sliding of large sections of the sides at the highest part of the mound. Its designed dimensions would have been significantly smaller than its present extent, but recent excavations have revealed that slumping was a problem even while the mound was being made.

The American Bottom is the flood plain of the Mississippi River in the Metro East region of Southern Illinois, extending from Alton, Illinois, south to the Kaskaskia River. It is also sometimes called "American Bottoms". The area is about 175 square miles (450 km), mostly protected from flooding in the 21st century by a levee and drainage canal system. Immediately across the river from St. Louis, Missouri, are industrial and urban areas, but nearby marshland, swamps, and the Horseshoe Lake (which was created by the river) are reminders of the Bottoms' riparian nature.

This plain with its rich alluvial soil, served as the center for the pre-Columbian Cahokia Mounds civilization, and later the French settlement of Illinois Country. Deforestation of the river banks in the 19th century to fuel steamboats had dramatic environmental effects in this region. The Mississippi River between St. Louis and the confluence with the Ohio River became wider and more shallow, as unstable banks collapsed into the water. This resulted in more severe flooding and lateral changes of the major channel, causing the destruction of several French colonial towns, such as Kaskaskia, which relocated; Cahokia, and St. Philippe, Illinois.