The Cahokia Mounds State Historic Site in Illinois features archaeological remains from the most sophisticated prehistoric native civilization north of Mexico. 

The 2,200-acre site located across the Mississippi River from St. Louis has preserved about 70 of the 100+ earthen burial and ceremonial mounds known to be built by the Mississippians who lived in the area from about A.D. 700 to A.D. 1400. 

Now a team of geodetic surveyors from NGA and graduate students from Saint Louis University (SLU) are using Unmanned Aerial Systems, or UAS, and Light Detection and Ranging technology, known as LiDAR, to find out if even more mounds or other archaeological structures lie within the acres of thick forests and swampy land near the site’s main complex.

In October, the NGA-SLU team conducted mobile LiDAR and UAS LiDAR surveys at the Cahokia Mounds site. The LiDAR UAS platforms were flown 250 feet above the ground. 
LiDAR is an optical remote sensing technology that can be particularly useful to find undiscovered archaeological features because it can penetrate forest canopies.  LiDAR technology provides the ability to create high-resolution digital elevation models of archaeological sites that can reveal micro-topography that are otherwise hidden by vegetation and difficult to distinguish through regular aerial photography or ground surveys. 

The team surveyed the entire Cahokia Mounds site, but largely focused on forested, swampy and unexplored areas on the southern side of the CSX Railroad tracks that bisect the property, said NGA’s UAS Program Manager Philip “Casey’’ Shanks, a geodetic surveyor in its Office of Geomatics.

“You can’t really even walk through some of that part,’’ he said. “That’s why the UAS is the right tool for the job.’’

Researchers at SLU and the Taylor Geospatial Institute, a consortium of eight Midwestern research and academic institutions, will be responsible for thoroughly analyzing the collected topographic data from Cahokia Mounds.

As part of their Cahokia Mounds work, the team also has:

• Established geodetic control monumentation throughout the site to provide permanent markers for other researchers and surveyors to use in the future.
• Re-surveyed nine monuments that had been used in a previous University of Illinois survey.
• Created a photogrammetric 3D foundational mesh model of Monks Mound, the largest earthen structure at Cahokia Mounds.

The Cahokia Mounds aerial survey, which covered an area roughly 2 kilometers by 2 kilometers, marked the largest single area NGA has ever surveyed with UAS LiDAR, said Stacy “Craig’’ Ackermann, a geodetic surveyor and LiDAR SME in the Office of Geomatics. 

It also was a fun and welcome opportunity to expand the range of work the NGA surveyors typically do and to interact with graduate students pursuing geospatial studies.  “The best part was applying our tradecraft in a way that is not the norm for us – in this case it was archaeology – and teaching the tradecraft,’’ Ackermann said.

The geodetic surveying project was done through an existing Cooperative Research and Development Agreement between NGA and SLU and in support of November’s Native American Heritage Month, said Todd Johanesen, director of NGA’s Source Foundation GEOINT Group. Johanesen also is co-senior champion for NGA’s American Indian Council. 

“This collaboration truly has been a meaningful one for all of those involved,’’ Johanesen said. “It has provided a wonderful opportunity for our folks to apply their expertise, work closely with a valued academic partner and make a significant contribution to our past, present and future communities.’’ 

The Cahokia Mounds site has been studied for some time, but much of its history remains unknown or has been lost over the years to erosion and modern agriculture, said Justin Vilbig, who is a geospatial data scientist at the Taylor Geospatial Institute and the SLU Ph.D. student leading the university’s work at Cahokia. The sprawling ancient city included dozens of burial and ritual mounds – some topped with temples or homes of leaders; causeways connecting some of the structures; and borrow pits, where the earth was dug to build the mounds and then often used as trash dumps.

“There are a lot of questions about Cahokia’s past that can be answered by remote sensing and LiDAR data," Vilbig said. “This gives the full landscape – where features were in context with each other – and what were the priorities of the Cahokians.’’

From a storytelling perspective, Vilbig hopes the NGA-SLU work can not only shed more light on the full layout of the ancient city, but also indicate more clearly how its people lived. From a modern practical perspective, he believes the work will help with site preservation and provide guidance to other researchers about where best to pursue or not pursue excavation for further study.

Owned and managed by the state of Illinois, Cahokia Mounds is both a National Historic Landmark and a UNESCO World Heritage site. The site, located near the city of Collinsville, Ill., features dozens of preserved mounds, including the multi-terraced Monks Mound, the largest earthen, man-made mound in North America.  

Once one of the greatest cities of the world, Cahokia was a bustling center of trade and had a population of about 15,000 to 20,000 people at its peak from A.D. 1100 to A.D. 1200. Although not as well-known as the Mayan, Incan and Aztec civilizations of Central and South America, Cahokia’s urban settlement near the Mississippi, Illinois and Missouri rivers rivaled those Mesoamerican cultures and thrived centuries before Europeans arrived in the New World.