Corn may seem like an odd foundation on which to build an empire. But the cultivation of corn was largely responsible for the development of Cahokia, a city built by a group belonging to what we now call the Mississippian culture that flourished a thousand years ago in the valleys and plains of the Midwest.

Corn that could be grown and eaten, and more importantly, stored and traded, enabled hunting and gathering tribes to settle in one place, where they could build cities, develop more elaborate rituals and ceremonies, create works of art and permanent structures.So it was at Cahokia, located near Collinsville in southern Illinois, eight miles across the river from St. Louis.

In its day - from about 700-1400 A.D. - Cahokia was the largest prehistoric settlement north of Mexico. At its peak, from 1100-1200, it may have housed as many as 20,000 people.

They were mound-builders, constructing earthenware mounds not only as burial sites but also as platforms for wooden temples and palaces. Had they built with stone, Cahokia would rival the great pyramids of Mexico and ruins of Central America. But wood rots and earthworks are harder to decipher, and it was not until considerably later that the mounds were recognized as the man-made structures they were and the scope of the city defined.

In 1982 Cahokia was recognized by UNESCO as a World Heritage Site. The 2,200-acre location is administered by the Illinois Historic Preservation Agency. A large interpretive center opened in 1989 and offers a film and life-size replicas of houses and buildings as well as displays of artifacts and other exhibits. Three marked trails take visitors around many of the 80 mounds that are left (originally there were about 120), and a six-mile nature hike/cultural trail provides a more complete look at the area. Tapes are available for self-guided tours.

The people who lived here left no written language, so much of their story has had to be pieced together from excavations and artifacts. Only 1 percent of the area has been uncovered, and many mysteries remain. But historians and archaeologists have been able to put together a fairly good picture of the past.

There is no record of what the people called themselves or their city. The Mississippian name comes from the geologic period when the culture was at its height. Cahokia was first used in 1800 to commemorate a later group of Illini Indians. (The first Europeans didn't come into the area until about 1600, some 200 years after the original dwellers were gone.)

The Mississippians were agriculturists, growing not only corn but also squash, pumpkins and sunflowers, carefully tended with hoes made of chert blades strapped to wooden handles. This diet was supplemented with meat from deer and waterfowl. But almost all the pottery and figurines found here seem to be tied to agriculture and fertility rather than to warfare, in contrast to many other cultures of the time.

Houses, scattered about at the base of the mounds, were primarily one-family dwellings. They and the larger ceremonial buildings were probably made with a pole framework, prairie grass thatched roofs and mats or clay plaster to cover the walls. Most of the people were buried in cemeteries, but some important figures seem to have been buried in some of the mounds. Mounds of conical, platform and ridgetop shapes were built, and investigations suggest there was more than just random placement of the piles of earth.

The greatest of the mounds, now called Monks Mound, rises in terraces to 100 feet - about the height of a 10-story building. The base covers 14 acres, making it the largest prehistoric earthen structure in the Western Hemisphere.

Today, a wooden staircase of 144 steps leads to the top, where there is a view of a part of the wide Mississippi floodplain known as the American Bottom. At one time, excavations reveal, a large building about 105 feet long by 48 feet wide and perhaps 50 feet high stood at the top, probably the home/temple of the primary chief.

Monks Mound was built, basketfuls of dirt at a time, over a period of 300 years. In all, it probably took 15 million basketfuls of dirt, but there was more to the building of a mound than mere piling up of earth. Core samples show that different kinds and textures of dirt were used to give the mound drainage and proper stability.

Another accomplishment of this civilization was the construction of a sun calendar known today as Woodhenge. This circle of large red cedar posts surrounding a central observation point, about half a mile west of Monks Mound, tracked the movement of the sun throughout the year. Excavations reveal that the circle was built at least five times during the 700-year history of Cahokia, each time with a different diameter and a different number of posts, so there may have been purposes other than astronomical ones associated with it. The circle that has been reconstructed was the third circle, built with 48 posts and a diameter of 410 feet.

Archaeologists have also uncovered evidence of a wooden stockade, with walls 12 to 15 feet high, that surrounded about 300 acres of the central city. It was replaced at least four times during the time of occupation, leading to speculation that conflict, warfare and a need for protection were part of life here. There was also an open plaza at the center of town, most likely used for athletic contests and games such as "chunkey," which involved throwing javelins at rolling pieces of stone.

In 1150 A.D., at its peak, Cahokia was larger than London of 1150 A.D. Not until 1800 would the United States have a city (Philadelphia) to equal the size of Cahokia at its peak. Even more remarkable is the fact that Cahokia was built entirely by hand; no evidence has been found of beasts of burden or of development of the wheel. Stone axes were used to chop down trees, and human power moved them into place.

Despite some similarities, there is also no evidence that the Mississippians had any direct contact with the great civilizations of Mexico and South America; historians think the groups developed independently. There is proof, however, that the people at Cahokia had an extensive trade network. Artifacts found here include objects made of copper from the upper Great Lakes region, mica from the Appalachians and whelk, conch and other shells from the Atlantic seaboard.

Cahokia was unique among other Mississippian settlements that have been found throughout a territory stretching from Minnesota to Florida. But was it a place apart, or was it the capital of this empire? Historians don't know. They also aren't sure which groups, if any, are the descendants of these people.

Nor do they know exactly why this civilization faded away. But they sense that a gradual decline - rather than epidemic, invasion or disaster - ended life here.

They do know that by 1400, the area had been abandoned. There may have been some climatic changes, but the most likely cause for Cahokia's demise was its success, which in turn led to over-exploitation of natural resources. Historians figure it would have taken 20,000 trees to build the stockade one time, for example; and as trees were cut down, so was the habitat of animals that could be used for food.

Corn, too, may have played a part. Ironically, the corn that enabled the civilization to grow and prosper would, over time, deplete the soil. And a diet of too much corn, and too few other nutrients, could lead to malnourishment and disease.

In the end, it was probably a civilization that collapsed under its own weight, leaving much mystery buried in its mounds.

Today, Cahokia is a quiet, peaceful place. Trees and grass grow around and over the mounds. The sound of songbirds echoes in the air. And lessons about the overuse of resources blend gently with admiration for what the civilization accomplished a thousand years ago.

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ADDITIONAL INFORMATION

If you go

Cahokia Mounds State Historic Site is open daily, except some holidays, from 8 a.m. to dusk. The interpretive center is open daily from 9 a.m. to 5 p.m. The suggested donation is $2 for adults and $1 for children. For information, call 618-346-5160.

Other sites within a day's drive of Collinsville in addition to St. Louis include Springfield, Ill., one-time home of Abraham Lincoln, the Mormon historic sites at Nauvoo and Carthage, and Hannibal, Mo., Mark Twain's hometown.