National Geographic News
Early morning aerial photos of Cahokia Mounds State Historic Stie.

Cahokia Mounds State Historic Site holds the remnants of the largest and most influential city of the mound-building Mississippian culture.


Glenn Hodges

for National Geographic

Published March 7, 2014

A thousand years after the Native American city known as Cahokia sprouted on a floodplain east of modern-day St. Louis, Missouri, the story of its explosive birth and precipitous decline remains one of America's great mysteries. (Read "Cahokia: America's Forgotten City" in National Geographic magazine.)

But a new study published in the Journal of Archaeological Science may shed fresh light on how this city of thousands—perhaps 20,000 or more—formed in a matter of just 50 years.

By examining the strontium content of teeth from the remains of 87 ancient Cahokians and comparing it to the strontium signatures of local fauna, a team led by Thomas Emerson of the University of Illinois at Urbana-Champaign has concluded that at least one-third of Cahokia's residents immigrated from areas outside the floodplain known as the American Bottom.

How did they reach this conclusion, and what might this mean for our understanding of Cahokia? In an interview earlier this week, writer Glenn Hodges posed these questions to Emerson, who is also the Illinois State Archaeologist.

Map of the eastern United States, showing  Mississippian culture area of influence, and locating Cahokia. Illustration of what Cahokia looked like.

First of all, how do strontium signatures work?

Essentially, it works under the principle that you are what you eat. Strontium is in the bedrock across the world. It dissolves into the water supply, the water is absorbed by animals and plants, humans consume the animals and plants, and the strontium moves into their bones and teeth.

Strontium varies by the kind of bedrock, and that's what allows us to use strontium to tell where somebody was raised. To determine the signature for Cahokia, we used small mammals that probably never moved more than a mile from where they were born—squirrels, rabbits, etc.

Cahokia Indians devoted their time to ambitious building projects, specialized crafts and ceremonies.
The ancient Cahokians were expert builders and craftspeople.

So you take that animal data as a baseline, and compare it to the strontium in people's teeth.

Yes. There's one set of teeth that matures when you're about five or six, and there's a second set that matures between six and sixteen. So we're looking at people whose infant teeth indicate they were living in a different place, but by the time they became teenagers they were living in Cahokia. Once you move beyond that 16-18 age group, we can't recognize immigrants anymore.

How did you extrapolate from 87 individuals to one-third of the population?

You have to assume that your sample is representative. We accessed almost all the individual remains that are held in institutions. The population available for testing is just that small.

A reconstructed section of stockade protected Cahokia from attack.
This reconstruction shows the type of stockade that protected the city from attack.

So if one-third of your sample immigrated in their youth, the actual proportion of immigrants might be higher? Because you've got to figure that these kids came with parents who already had all their adult teeth.

Yes. So the numbers are probably higher. We just have no way to get at that right now.

Do you have any idea where the immigrants were from, or do you only know that they're not from the Cahokia area?

Our level of research right now is confined to identifying immigrants. To understand where they came from, we have to greatly expand the database of strontium throughout the mid-continent, and that research has not been done yet.

Is that research anywhere on the horizon?

Yes, it is. We started it in 2009 with preliminary work, and now we're looking to expand that database.

How long do you think it will take to get a useable database?

Probably two to three years. It's basically getting the right kind of samples and getting them processed. Of course, we have to get the money to do it, but the research is fairly simple.

Figurine of a chunkey player rolling his stone along the ground.
This figurine represents a man playing chunkey, a game that originated in the Cahokian area.

So how does this change the picture we have of Cahokia? Wasn't it already thought that immigration was a factor in its explosive growth?

It depends on who you talk to. There's still a group of archaeologists thinking in pretty traditional terms—yeah, there were some immigrants, but it was pretty much a homogeneous population getting larger.

But when you start thinking about Cahokia as multiethnic and probably multilinguistic, with massive population growth and nucleation [forming around a central area], you have to ask: What sort of social, religious, and political organization do you need to actually make that function? When people don't have anything in common, how do you create unity?

In terms of research, it's a sea change. Now we can look at Cahokia in comparison with the growth of cities all over the world. From other areas we know that's how cities grow, by immigration. I don't care if you're looking at Roman London, or Delhi, or some of the big Chinese cities, they're actually nucleations of dissimilar people.

So this kind of takes Cahokia out of this romantic mythology of the Indian past, and shows how these people were facing the same kind of problems as people all over the world do when you begin to urbanize. It allows you to do cross-cultural comparisons with a lot more validity.

So you're really talking about expanding the scope of Cahokia research, and connecting it with this larger body of scholarship?

There are basically two schools of thought. One is based on very localized interpretations and perspectives of Cahokia, and the other sees Cahokia as a player in international research.

And you think the balance is shifting to the latter?

I think ultimately it will be the dominant perspective on Cahokia.

Larry Gil
Larry Gil

Fascinating, have they determined any genetics from the teeth?

Robert Brinar
Robert Brinar

This is a subject that has fascinated me for a long time. Who were they and where did they come from?

E James
E James

There is a bit of imprecise language (and dumbing down) here that obscures the methods used. "By examining the strontium content of teeth from the remains of 87 ancient Cahokians..." implies that the amount of strontium in teeth is what is measured.  It's the ratios of strontium isotopes that are being measured. The use of the word "isotope" is avoided throughout the article and thus a teachable science moment was missed.

Nat Turner
Nat Turner

Of course the international connection cannot be ruled out when one notes the similarity of these structures to step pyramids and therefore the wider world pyramid building cultures

Robert Dykstra
Robert Dykstra

Always great to get an update on Cahokia.  But when is some zillionaire going to give money to get rid of those ghastly highways that continue to disfigure the site?  I doubt that local government or the State of Illinois (or certainly Congress) would get together the funding -- or the courage -- to do what needs to be done about rerouting traffic, as has been done elsewhere (e.g., Stonehenge, I think)..  

Gwendolyn Mugliston
Gwendolyn Mugliston

I wish I had known about this sort of work and research when I was young.  How fascinating.  Maybe it is fascinating now because of the research that was done during the years I was doing something else.  Anyway...strontium dating teeth from Native Americans  long dead would probably be difficult due to the cultural taboos regarding burial and burial sites of Native Americans.  But animals...that is possible.  This will be a very interesting ongoing story over the next many years. 


Picnicked there as a child--a place of some wonderment---surrounded by deplorable slums of modern times.

Rita Kenion
Rita Kenion

@Robert Brinar  How far back do you want to go?  Originally across the Bering Straits, like everyone else who lived here? Millions and millions of First Americans preceded the inhabitants of Cahokia and the other  Mississippian sites.

Brian Roderick
Brian Roderick

@Robert Dykstra  The Cahokia site has come a long way, In 1970 it was little more than a side show attraction and now it is a secured site with a nice museum and tons of research completed. We have to give credit where credit is due would be hard to get the interstate hwy rerouted especially going into ST Louis and between several large bodies of water. 

Andrew Booth
Andrew Booth

@Gwendolyn Mugliston Why should it be that difficult? Many similar strontium and DNA studies have been conducted on ancient burials here in the UK and the results have been fascinating. 

Many of the Paleolithic, Mesolithic, Neolithic and Bronze Age skeletons in the UK are not of people born here but of people who were born in different areas of Europe and further afield who travelled great distances before they died here. Rather than the prehistoric British population being insular and sedentary such studies have revealed an extensive continental trade network based on copper with prehistoric Britain also having contacts with the Mediterranean, North Africa and the Middle East. Indeed, several ancient skeletons originated there. Conversely, the studies have also shown how many British people today are closely related to ancient skeletons that have been found in their local area - including the Paviland skeleton which is 25,000 years old!

I'm sure that studies of early American skeletons would reveal equally fascinating results.    

Angi Gray
Angi Gray

It is difficult in the US because of laws and treaties that restrict non-consensual curation or testing on Native American remains. If as associated living tribe can be identified or extrapolated, the remains must be turned over to that tribe for reburial unless the tribe consents Otherwise (which they as yet have not done, thanks to previous poor relations between tribes and scientists).


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