Cahokia

Cahokia preserves the remains of a Native American city that flourished from about 1050 to 1350 CE on the floodplain of the Mississippi River in south-western Illinois, across the river from modern St. Louis. It was the largest and most influential settlement of the Mississippian culture, and its great earthen mounds, above all Monks Mound, make it the largest pre-Columbian earthwork site in the Americas north of Mexico. Its original name is unknown; it is called after the Cahokia, an Illinois people who lived in the area centuries after the city was abandoned.

People lived in the area long before the city existed, and a settlement stood at Cahokia from around 600 CE. Before about 1000, the local population lived in small villages of fifty to a hundred people, moving every few years, and maize was only a minor crop, introduced around 900. Around 1050 this changed abruptly, in what archaeologists sometimes call the "Big Bang". A planned layout aligned to the cardinal directions was laid over the older villages, with a vast central plaza, a raised causeway and dozens of mounds, and pottery and building styles became uniform across the region.

The growth was driven partly by immigration. Pottery from the lower Ohio, the lower Mississippi, the Upper Midwest and the southern plains appears at this time, and burial studies show that many residents were born elsewhere. Population estimates for the peak vary widely, from about 6,000 to as many as 40,000; the higher figures would make Cahokia larger than any later city in the United States until Philadelphia passed 40,000 in the 1780s.

At its height around 1100 the city covered some fifteen square kilometres and had about 120 earthworks. Monks Mound, built up in as many as ten stages, rises about 30 metres and covers some 5.6 hectares; a large building, perhaps a temple or a chief's residence, once stood on its summit. West of Monks Mound lay a series of timber circles, the so-called Woodhenges, each larger than the last, whose possible astronomical role is still studied.

Mound 72, a burial mound south of the centre, held about 270 people. One man was laid on a bed of some 10,000 shell-disc beads arranged as a falcon, and many others appear to have been sacrificed, including a group of more than fifty young women. Cahokia's trade reached the Great Lakes and the Gulf Coast, bringing copper, chert hoes, shark teeth and seashells, and a copper workshop excavated near Mound 34 is the only one known from any Mississippian site. The historian Daniel Richter has noted that the city's peak coincided with the rise of Chaco Canyon in the south-west.

Around 1160 to 1170 fire destroyed a residential compound, enclosed by walls, in the East St. Louis precinct, possibly in unrest, and around 1175 a palisade with bastions was built around the core, later rebuilt several times on a smaller line. People began leaving in the late twelfth century; by the mid-thirteenth the population had fallen by at least half, and by 1350 the city was empty. Scholars have proposed many causes, including drought and flooding, warfare, disease, a diet too dependent on maize, and tensions within a mixed immigrant population. Some argue that claims of human-caused environmental damage lack evidence, and most see several factors working together.

The surrounding region, known as the Vacant Quarter, had no substantial settlement from about 1400 to 1600. Ponca oral tradition recalls a time spent at the city, and Algonquian peoples of the Illinois Confederation moved into the area in the mid-seventeenth century.

French settlers claimed the land in the eighteenth century, and Trappist monks lived briefly on the site around 1809, giving it its modern name. Across the river, most of the related mounds of St. Louis were levelled for fill in the nineteenth century as the city grew. Illinois began protecting Cahokia in 1923 by authorising a state park, but highway building in the 1950s damaged parts of the site, even as it funded emergency excavations, including the 1960s digs by Warren Wittry that found the Woodhenge. Cahokia became a National Historic Landmark in 1964 and a UNESCO World Heritage site in 1982. It is managed by the Illinois Historic Preservation Division, and Native American nations, the Osage among them, work with archaeologists and continue to treat it as sacred ground in what is now the United States.