Mammoth Cave (left) photograph courtesy of the National Park Service. Everglades National Park (right) photograph courtesy of the National Park Service.
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World Heritage Sites in the United States

Cahokia Mounds State Historic Site
Collinsville, Illinois
Monks Mound depicted, the largest man-made earthen mound in North America. Photo courtesy of the U.S. Department of Transportation Federal Highway Administration

Cahokia is located east of St. Louis, Missouri
Courtesy of Cahokia Mounds State Historic Site

Cahokia Mounds State Historic Site is located in Illinois, just several miles east of the Mississippi River and St. Louis, Missouri.  The mounds are a unique example of a large American Indian cultural and urban complex that flourished between A.D. 1000 and 1350. The original complex of mounds, homes, and farms, covered over 4000 acres. Population estimates for Cahokia proper now range from 10-20,000. If East St. Louis, St. Louis and other surrounding sites are included, then a population of 40-50,000 is possible for "Greater Cahokia."

The site was once the largest indigenous urban center in what is now the United States, before the arrival of European explorers and settlers. Other large mounds were also located on the eastern and western sides of the river in what is now East St. Louis and St. Louis. However, most if not all of these mounds have fallen in the past 300 years to the development of these cities.

The earthen mounds at Cahokia offer some of the most complex archaeological sites north of Central Mexico.  Monks Mound, which dominates the World Heritage Site and is located near its center, is the largest manmade structure north of Central Mexico. Monks Mound measures 304 meters (1000 feet) by 213 meters (700 feet) at its base and covers 5.7 hectares (14 acres), rising to approximately 100 feet in a series of four terraces. Cahokia Mounds was the regional center for the American Indian Mississippian culture, resembling a modern metropolis with its complex social system and large, permanent, central towns. Cahokia Mounds World Heritage Site represents a truly unique example of the complex social and economic development of pre-contact indigenous Americans.

One fascinating aspect of Cahokia is that a circle of wooden posts once stood about one-half mile west of Monks Mound that aligned with the movements of the sun throughout the year. Archeologist Warren Wittry discovered this phenomenon in the 1960s after he identified a pattern of mysterious oval pits, arranged in circular arcs, at the site. Wittry reconstructed a series of wooden posts at the pits and then observed sunrises and their alignments with the posts. He determined that these posts appeared to predict the movement of the sun. He theorized that this served as a calendar. Upon further analysis, Wittry realized that both the posts and Monks Mound were shaped and placed in the exact spots necessary for the sun to look like it was rising from Monks Mound itself when the equinox occurred.

The Cahokia Mounds State Historic Site Interpretive Center offers visitors orientation at its theater and exhibits. The interpretive center features recreations of life and architecture at Cahokia during its heyday, based on the theories and discoveries of historians and archeologists.

Plan your visit

Cahokia Mounds State Historic Site, a World Heritage Site, is located at 30 Ramey St., Collinsville, IL. Cahokia Mounds State Historic Site is also a National Historic Landmark. Click here for the National Historic Landmark registration file: text and photos. Cahokia Mounds State Historic Site visiting days and times are subject to change, so contact the park ahead of time to make sure it will be open when you plan to visit. For more information, visit the Cahokia Mounds State Historic Site website or call 618-346-5160.

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