Cahokia Mounds, Illinois – Largest Archaeological Site in North America
Nestled near Collinsville, Illinois, a mere stone’s throw across the Mississippi River from St. Louis, Missouri, lies a sprawling testament to a sophisticated prehistoric civilization: the Cahokia Mounds State Historic Site. This expansive area, encompassing over 2,000 acres, safeguards the remnants of what is considered the largest and most complex archaeological site north of Mexico. Within its boundaries lie the silent echoes of a vibrant city built by the ancient Mound Builders, a civilization whose ingenuity and societal structure continue to fascinate and challenge modern understanding.
The story of Cahokia Mounds is one etched in earth. The site is characterized by monumental earthen structures, the most striking feature of this ancient urban center. Inhabited from approximately A.D. 700 to 1400, Cahokia Mounds flourished for centuries before its eventual decline and abandonment. Initially, the settlement was relatively small, with an estimated population of around 1,000 inhabitants. However, around the 11th century, a dramatic transformation occurred, leading to a population boom that swelled to tens of thousands.
At its zenith, between 1100 and 1200 A.D., the city of Cahokia Mounds sprawled across nearly six square miles, supporting a population estimated to be as high as 100,000 individuals. This makes it one of the largest pre-Columbian settlements in North America. The city was meticulously planned, with houses arranged in organized rows around open plazas, creating communal spaces for social interaction and public gatherings. Surrounding the urban core were agricultural fields and smaller satellite villages, providing sustenance and resources to the bustling metropolis. The Cahokians were also adept traders, establishing connections with other tribes as far away as Minnesota, facilitating the exchange of goods and ideas across vast distances.
Intriguingly, the original name of this impressive city remains shrouded in mystery. The inhabitants of Cahokia Mounds did not leave behind any written records, and their true self-designation has been lost to time. The name "Cahokia" is derived from a later, unrelated tribe that inhabited the region when French explorers first arrived in the late 17th century. The name, therefore, is a historical convenience, a label applied centuries after the civilization’s demise.
The defining characteristic of Cahokia is undoubtedly its monumental earthworks. These ancient Native Americans constructed over 120 earthen mounds within the city limits, 109 of which have been meticulously documented. Today, 68 of these mounds are preserved within the boundaries of the historic site, offering visitors a tangible connection to the past. It is believed that many more mounds were either altered or completely destroyed by subsequent agricultural activities and modern construction.
The mounds themselves vary dramatically in size and shape. Some are subtle rises in the landscape, barely discernible to the untrained eye. Others, however, are imposing structures, reaching heights of over 100 feet, dominating the surrounding terrain. The construction of these massive earthworks was a monumental undertaking, requiring the movement of an astonishing amount of soil. It is estimated that over 50 million cubic feet of earth were transported to the construction sites, primarily by human labor, using baskets to carry the soil on their backs. The extraction of this earth left behind large depressions, known as borrow pits, which are still visible throughout the area, serving as a stark reminder of the immense effort required to build Cahokia.
The mounds served a variety of purposes within Cahokian society. Archaeologists have identified three primary types of mounds: platform mounds, conical mounds, and ridge-top mounds. Platform mounds were the most common type and are believed to have served as foundations for monumental structures, including temples, residences of elite members of society, and spaces for political and religious ceremonies. These elevated platforms would have provided a commanding view of the surrounding landscape and served as symbolic centers of power. Conical and ridge-top mounds, on the other hand, were primarily used as burial locations or to mark important locations within the city. These mounds often contained elaborate burials, providing valuable insights into Cahokian beliefs about death and the afterlife.
At the heart of the Cahokia Mounds State Historic Site stands Monks Mound, the largest earthwork and the undisputed centerpiece of the ancient city. Rising to a height of 100 feet, it is the largest prehistoric earthen mound in North America, a testament to the engineering prowess and organizational capabilities of the Cahokia people. The mound measures an impressive 1,000 feet in length and 800 feet in width, covering an area of approximately 14 acres. It is comprised of four distinct terraces, each of which was likely added at different stages of construction, reflecting the city’s evolving architectural vision. It is estimated that the construction of Monks Mound required the movement of approximately 22 million cubic feet of earth, a truly staggering feat of engineering.
The name "Monks Mound" is a relatively recent designation, derived from French Trappist monks who resided nearby in the early 1800s. However, its true significance within Cahokian society is far more profound. Archaeologists believe that Monks Mound was likely the residence of the principal ruler of Cahokia, serving as a focal point for governance, religious ceremonies, and social gatherings. From this elevated platform, the ruler would have overseen the city, conducted important rituals, and made decisions that shaped the lives of thousands of people. Over the centuries, Monks Mound has been subjected to significant erosion and damage, both from natural processes and human activity, making it difficult to fully reconstruct its original form and appearance.
Surrounding Monks Mound and the central core of the city was a two-mile-long stockade, complete with strategically placed guard towers every 70 feet. This imposing defensive structure is believed to have been constructed on four separate occasions, each rebuilding requiring nearly 20,000 logs. The stockade served multiple purposes within Cahokian society. Primarily, it provided a crucial line of defense against potential invaders, protecting the city’s inhabitants and resources. However, it also served as a social barrier, separating the elite members of society from the common people, reinforcing the hierarchical structure of Cahokian society. Today, several sections of the stockade have been painstakingly reconstructed, offering visitors a glimpse into the defensive capabilities of this ancient city.
In addition to its monumental earthworks, Cahokia also boasts evidence of sophisticated scientific knowledge and engineering practices. Archaeologists have discovered four, and possibly five, circular sun calendars, often referred to as Woodhenge. These structures consisted of evenly spaced log posts that were carefully aligned to mark the changing seasons, solstices, and equinoxes. Woodhenge demonstrates an impressive understanding of astronomy and the cyclical nature of time, allowing the Cahokians to accurately track the passage of the year and plan their agricultural activities accordingly.
One of the most intriguing and unsettling discoveries at Cahokia was made on a small ridgetop mound known as Mound 72. Here, archaeologists unearthed the remains of nearly 300 individuals, predominantly young women, who are believed to have been sacrificial victims. The circumstances surrounding their deaths suggest a ritualistic practice, possibly intended to appease deities or ensure the prosperity of the city. Nearby, archaeologists discovered another grave containing the remains of a male individual, estimated to be around 45 years of age. This individual was laid upon a bed of 20,000 marine shell disc beads, indicating his high status within Cahokian society. It is believed that many of the other bodies buried near him were sacrificed to serve him in the afterlife, highlighting the complex and often brutal nature of Cahokian religious beliefs.
Further excavations at Mound 72 revealed another unsettling mystery. The remains of four men were uncovered, their heads and hands missing from their graves. The reason for this mutilation remains unknown, sparking speculation about possible ritualistic practices or acts of violence. The burial site is estimated to date back to around 950-1000 A.D., providing a glimpse into the early stages of Cahokian society.
Recent archaeological investigations at Cahokia Mounds continue to yield valuable insights into the city’s history and culture. In June 2024, Saint Louis University professors and students unearthed several 900-year-old ceramics, microdrills, walls, and trenches dating from around 1100 to 1200 AD. These discoveries, reported by Heritage Daily, are the result of an aerial survey conducted by SLU and the National Geospatial-Intelligence Agency using Unmanned Aerial Systems (UAS) equipped with Light Detection and Ranging (LiDAR) technology. The LiDAR survey was designed to identify potential mounds or archaeological features hidden within the thick forests and swampy land surrounding the site’s main complex.
Despite its impressive scale and sophistication, Cahokia experienced a gradual decline in population beginning sometime after 1200 A.D. By the 1400s, the entire site had been abandoned, leaving behind a silent testament to a once-thriving civilization. The reasons for this decline and abandonment remain a subject of ongoing debate among archaeologists. Theories include climate change, warfare, disease, drought, and resource depletion.
Perhaps even more puzzling is the absence of any legends, records, or mentions of Cahokia in the lore of other local tribes, including the Osage, Omaha, Ponca, and Quapaw. This strange silence has led some experts to theorize that something particularly dreadful occurred at the site, something that the other tribes wished to forget.
Today, many people still consider the Cahokia site to be a sacred place. Native Americans and metaphysical groups believe that Cahokia is a source of powerful psychic energy, attracting visitors from all walks of life who seek to connect with the past and experience the spiritual essence of this ancient city.
The Cahokia Mounds State Historic Site was designated a National Historic Landmark in 1964 and a World Heritage Site in 1982, recognizing its outstanding universal value. The site offers a variety of special events, craft classes, lecture series, tours, and other programs throughout the year, providing visitors with opportunities to learn about the history, culture, and significance of Cahokia. Located just outside of Collinsville, Illinois, a short distance off Interstates 55/70 and 255, along Route 40, the highway bisects the area, separating Monks Mound from the Interpretive Center. This unique location makes it easily accessible for those wishing to explore this remarkable archaeological site.