Cahokia was once a native urban settlement on the Mississippi River that still catches the intrigue of archaeologists, scholars, and the public today.  At the center of the city was Monks Mound (Figure 1).  This mound was “Cahokia’s great central pyramid” and was “the largest such monument in North America” (Pauketat 2009, 26).  Surrounding Monks Mound is four plazas, each named for their location relative to the city’s center.  Though experts thought they reasonably understood the mound and plazas, a new discovery complicates matters.

Figure 1. Monks Mound today with a constructed staircase and other structural supports as preventative measures for decay. The mound and its surrounding plazas are near the town of Collinsville, Illinois. Photograph by Emily Dickinson.

In the summer of 2022, geoarchaeologist Caitlin Rankin conducted an excavation in the north plaza.  She did this to test a hypothesis that originated from her observation of the plaza’s low elevation.  During the excavation, Rankin “extracted sediment cores around the four mounds that define the north plaza” (Yates 2022) (Figure 2).  She additionally collected topsoil samples from varying nearby environments so that a comparison could be made.  The different environments included wetlands, seasonal wetlands, and prairie.

Figure 2. Geoarchaeologist Caitlin Rankin standing in an excavation pit at Mound 5, where sediment analysis showed that the north plaza was a wetland in the times of Cahokia. Photograph by Caitlin Rankin.

The comparison between the topsoils and sediment cores revolved around carbon isotopes.  Rankin took stable carbon isotopes, which would include C12 and C13, from the topsoil and compared them to the carbon isotopes within the sediment cores (Yates 2022).  From this comparison, Rankin was able to “establish what kind of plants lived in the area – finding evidence for wetland plants” (Plaza In Ancient City 2022).  This discovery was vital because it meant that the north plaza was a wetland and most likely permanently submerged underwater.

With this new knowledge, archaeologists must rethink the meaning of the north plaza.  They must also try to determine how the underwater plaza could represent the cultural ideologies and practices of the Cahokians.  For the people of Cahokia, nature, the cosmos, and water were large areas of focus within their mythology and religion (Pauketat 2009).  Because of this, Rankin’s discovery may suggest that the plaza was constructed to honor the gods of Cahokia.  Just as Monks Mound was constructed to interconnect society with religion, now it can be seen that there was a potential religious and cultural motive in the construction of the plazas.

Besides morphing the interpretation of the Cahokian religious practices, the underwater aspect of the plaza also implies that the people of the city had techniques and construction methods to build in those conditions.  This, coupled with their calendar and mathematical capabilities, shows that Cahokia was a highly advanced and complex society that should garner the world’s respect today.  

Lastly, this discovery shows that archaeology is an ever-evolving process and that nothing is ever set in stone.  Rankin’s work will inspire more archaeologists to reevaluate Cahokia, leading to a better understanding of the ancient city.

Further Readings:

Rankin’s Official Report on Findings

New Insights Into Monks Mound At Cahokia

References:

Pauketat, Timothy R. 2009. Cahokia: Ancient America’s Great City on the Mississippi. New York, N.Y., Viking. 

“Plaza In Ancient City of Cahokia Near Today’s St. Louis Was Likely Inundated Year-Round.” National Science Foundation, sec. Research news. https://beta.nsf.gov/news/plaza-ancient-city-cahokia-near-todays-st-louis.

Yates, Diana. 2022. “North ‘Plaza’ in Cahokia Was Likely Inundated Year-Round, Study Finds.” Illinois News Bureau, sec. Research News. https://news.illinois.edu/view/6367/626821378.