The Significance of a North Plaza Discovery in Cahokia

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


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.

Yates, Diana. 2022. “North ‘Plaza’ in Cahokia Was Likely Inundated Year-Round, Study Finds.” Illinois News Bureau, sec. Research News.

The Importance of Radiocarbon Dating in Irish Archaeology

Radiocarbon dating is an archeological dating technique based on the radioactive decay of carbon-14 atoms (Renfrew and Bahn 2018, 108-140).  Ireland is a country where radiocarbon dating has been vital because of its climate, harsh weather patterns, and features.  Without this technique, key parts of Ireland’s history would continue to be murky or undetermined.

A recent find that involved the use of radiocarbon dating was that of a pagan deity statue (Figure 1), which gave insight into the religious and spiritual practices of the Irish people before St. Patrick made his way to the island (Gershon 2021).  Given that the excavation team found the statue in a bog, it was in excellent condition due to the natural preservation of the matrix.  

Figure 1. Archaeologist Cathy Morre standing next to the pagan deity statue found in a bog in Gortnacrannagh, Ireland. Photograph by Archaeological Management Solutions.

The process of radiocarbon dating involves finding an uncontaminated sample, running tests to determine the carbon-14 atoms’ decay level, and finally calibrating the found date to the modern time system (Renfrew and Bahn 2018, 108-140).  Once the samples from the statue went through this process, it was determined to be sculpted between 200 and 400 C.E. (Gershon 2021).  With this given time range, archaeologists could link together multiple ritualistic ruins and artifacts in the local area, allowing for a better understanding of the religious practices of the ancient Irish peoples.  Without radiocarbon dating, this would have been much more difficult to determine, and the time period of this site and others would be unclear.

Radiocarbon dating also helped immensely with dating ancient architecture in Ireland.  What has been learned from these sites has been essential for putting together a more accurate timeline of Irish civilization.  In 1992, Rainer Berger selected architecture, and then targeted the mortar within the infrastructures.  Specifically, he wanted to perform radiocarbon dating on the charcoal within the mortar to better understand when the buildings were constructed.  To isolate the carbon-14 atoms within the charcoal, the mortar was “treated with cold dilute hydrochloric acid until all inorganic carbonate [has] been destroyed” (Berger 1992, 882).  Once that step was complete, further cleansing commenced, eventually leaving just the desired atoms.  

The decay of the atoms obtained by Berger revealed that the small chapels, churches, and towers (Figure 2) he was analyzing were all constructed after the arrival of St. Patrick, meaning that they were made to withstand Viking attacks and raids during an era of violence and uncertainty.  This hints at cultural and societal values of the time, as well as the ‘why’ behind the unique architecture.  The accuracy of the radiocarbon dating also made it easier for archaeologists to individually order the buildings based on the time of construction, which was challenging to do in the past.

Figure 2. The Clonmacnoise Round Tower, one of the many sites throughout Ireland where   Carbon-14 isotopes were extracted from mortar. Photograph by Sarah Murphy.

All-in-all, this is just a glimpse into the vast array of archaeological progress that radiocarbon dating has catalyzed in Ireland.  As time goes on, radiocarbon dating will thicken Irish culture with layers of complexity and change how the history of Ireland is written.  




Further Readings:

Radical New History of Britain and Ireland Enabled by Precise Radiocarbon Dating

What Ancient Secrets Lie Beneath this Little-Known Irish Bog?


Berger, Rainer. 1992. “14C Dating Mortar in Ireland.” Radiocarbon 34 (3): 880–89.

Gershon, Livia. 2021. “Eight-Foot-Tall, 1,600-Year-Old Statue of Pagan Deity Found in Ireland.” Smithsonian Magazine, 2021, sec. Cool Finds.

Renfrew, Colin, and Paul Bahn. 2018. Archaeology Essentials: Theories, Methods, and Practice. Fourth edition. Thames & Hudson. 108-140.