Unearthing an ancient city with modern technology

Archaeologists are using modern technology to probe a historic city. St. Louis reporter Jim Kirchherr takes us to Cahokia State Historic site in Illinois, where recent excavations have revealed secrets about ancient civilizations.


Archaeologists are using modern technology to probe a historic city.

St. Louis reporter Jim Kirchherr takes us to Cahokia State historic site in Illinois, where recent excavations have revealed secrets about ancient civilizations.

Let's take a look.

They start showing up just after 5:00 a.m.

at the reconstructed circle of posts called Woodhenge at the ancient city known today as Cahokia Mounds.

This is the first day of summer.

That's why they've come.

Just to celebrate the solstice the same way that the old people used to.

Just something we wanted to do before we pass on.

The man with the stepladder is Bill Iseminger, site manager of the Cahokia Mounds State Historic Site.

He gives a talk here every solstice and equinox at this solar calendar built to mark the seasons and the rising sun.

First of all, for those who are not that familiar with our site, this is the largest prehistoric Indian settlement in America, the largest north of Mexico.

We'll see kind of the glow of the sun.

We may not see the actual ball of the sun because of the trees that have grown up.

And about 60 people showed up for this 5:20 sunrise.

It's likely a lot more than that witnessed the sunrise at this place a thousand years ago.

So we use the term city when we talk about Cahokia because it was so much bigger than anything else at that time or even for a long time after that.

It covered about 6 square miles, had about 120 mounds here, and at its peak, maybe anywhere from 10,000 to 20,000 people.

The excavations that have gone on at this site over the years, if you put them all together, probably less than 1% of the site has been excavated.

But when you think about how big the site is...

There are a lot of mysteries in this place.

This Mississippian metropolis was abandoned long before European explorers arrived to discover one giant earthen mound and many smaller ones.

Over time, some of the mounds were destroyed.

Artifacts were taken.

Fields were plowed.

Roads and highways and subdivisions were built.

Serious site preservation and archaeological study really didn't get under way here until the 1960's.

And now every year you'll find archaeological teams digging, searching, putting together the pieces of a very large and complex physical, social, and political puzzle with no written or direct oral history to guide them.

It is steady work.

Well, my eyes are always just searching the landscape.

John Kelly has been digging here for nearly 50 years.

So from basically early '60s and up to today working here, and there are other institutions, there's been continuous work.

I wouldn't say, there's probably hasn't been a year in which there hasn't been some kind of excavations being done at the site.

And the knowledge has given us a much clearer picture of this city -- the physical layout, the structures, the neighborhoods -- and the people from the great chief on the big mound to those who lived and worked throughout the city.

And yet there's so much more to find, and there are new ways to find it.

A team funded by the National Geographic Society was here surveying a field near the big mound with a magnetometer, which will indicate features below ground where soil has been disturbed, say, for the building of a house or a sweat lodge.

And this technology will basically pick up differences in magnetic properties to see where humans were altering the soils.

We can also use techniques like ground-penetrating radar, or GPR.

We did do a small section earlier this week of GPR.

At another dig directed by St. Louis University professor Mary Vermilion, they did an electrical resistance survey.

Probes run a current through the ground, and variations in electrical resistance produce a map and a pretty good idea of where you should dig.

This is the sweat lodge.


So that's pretty spectacular.

You can see it's 3 meters in diameter.

How much of this kind of technology is changing what archaeologists do and how they do it?

It's changing it drastically.

And now more and more before we start excavating, to be able to help us place where excavation units are, to save time, to save labor.

Archaeologists still use shovels and trowels and brushes, but they can now look into the ground before they dig.

But go around this little corner here.

John Kelly for years has been concentrating on mapping the stockade wall that once enclosed the big mound and its plazas.

But I think the most important thing for me as an archaeologist is actually seeing the way in which communities were laid out, but also how that space relates to their cosmology.

More than likely, the leader on top was thought to be related to or brother of the sun.

To have the sky brother coming out of his mound would reinforce his authority and power and his connection with the upper world.

There are a lot of questions we have about Cahokia and what happened here.

And through, you know, controlled excavations, we hope to answer a lot of those questions.