Cahokia (USA) - Massive Mississippian Center in the American Bottom

Was Cahokia's Rise and Fall Engineered by an Immigration "Problem"?

Cahokia Mounds State Historic Site
Monk's Mound at Cahokia Mounds State Historic Site. | Location: Collinsville, Illinois, USA. Michael S. Lewis / Getty Images

Cahokia is the name of an immense Mississippian (AD 1000-1600) agricultural settlement and mound group. It is located within the resource-rich American Bottom floodplain of the Mississippi River at the junction of several major rivers in the mid-central United States.

Cahokia is the largest prehispanic site in North America north of Mexico, a proto-urban center with numerous allied sites spread across the region.

During its heyday (1050-1100 AD), the urban center of Cahokia covered an area of between 10-15 square kilometers (3.8-5.8 square miles), including nearly 200 earthen mounds arranged around vast open plazas, with thousands of pole and thatch houses, temples, pyramidal mounds and public buildings laid out in three great planned residential, political and ritual precincts.

For perhaps no more than 50 years, Cahokia had a population of about 10,000-15,000 people with established trade connections throughout North America. The latest scientific research indicates that Cahokia's rise and fall were engineered by immigrants who together refashioned the Native American communities for the greater Mississippian culture. The people who left Cahokia after its breakup brought the Mississippian culture with them as they traversed throughout fully 1/3 of what is today the United States.

Cahokia's Chronology

Cahokia's emergence as a regional center began as a collection of rudimentary Late Woodland farming villages about 800, but by 1050 it had emerged as a hierarchically-organized cultural and political center, inhabited by tens of thousands of people supported by local plant domesticates and maize from Central America.

The following is a brief chronology of the site.

  • Late Woodland (AD 800-900) numerous small farming villages in the valley
  • Fairmount Phase (Terminal Late Woodland AD 900-1050), the American Bottom had two many mound centers, one at Cahokia and the Lunsford-Pulcher site, 23 km (12 mi) to the south, with a total population at Cahokia of around 1,400-2,800
  • Lohmann Phase (AD 1050-1100), Cahokia's Big Bang. Around 1050, there was a sudden growth at Cahokia with a population estimated between 10,200-15,300 people within an area of 14.5 sq km (5.6 sq mi). Changes concurrent with the population explosion included community organization, architecture, technology, material culture, and rituality, all of which likely involved in-migration from elsewhere. The site was characterized by large ceremonial plazas, post-in-circle monuments ("woodhenges"), dense habitation zones of elites and commoners, and a central core of 60-160 ha (.25-.6 sq mi) of at least 18 mounds surrounded by defensive palisades
  • Stirling Phase (AD 1100-1200), Cahokia still controlled the American Bottom, the lower portions of the Missouri and Illinois river floodplains and the adjacent hilly uplands, amounting to some 9,300 sq km (~3,600 sq mi), but the population was already in decline by 1150, and its upland villages were abandoned. Population estimates are 5,300-7,200.
  • Moorehead Phase (AD 1200-1350) Cahokia saw steep decline and final abandonment--the latest population estimates for the period are between 3,000-4,500

Greater Cahokia

There were at least three great ceremonial precincts within the region known as Greater Cahokia.

The largest is Cahokia itself, located 9.8 kilometers (6 miles) from the Mississippi River and 3.8 km (2.3 mi) from the bluff. It is the largest mound group in the United States, centered on an expansive 20 ha (49 ac) plaza fronted on the north by Monks Mound and surrounded by at least 120 recorded platform and burial mounds and lesser plazas.

The other two precincts have been impacted by the modern urban growth of St. Louis and its suburbs. The East St. Louis precinct had 50 mounds and a special or high-status residential district. Across the river lay the St. Louis precinct, with 26 mounds and representing a doorway to the Ozarks mountains. All of the St. Louis precinct mounds have been destroyed.

Emerald Acropolis

Within one day's walk of Cahokia were 14 subordinate mound centers and hundreds of small rural farmsteads.

The most significant of the nearby mound centers was likely the Emerald Acropolis, a special religious installation in the middle of a large prairie near a prominent spring. The complex was located 24 km (15 mi) east of Cahokia and a broad processional avenue connects the two sites.

The Emerald Acropolis was a major shrine complex with at least 500 buildings and perhaps as many as 2,000 during major ceremonial events. The earliest post-wall constructed buildings date to about 1000 AD. Most of the remaining were built between the mid-1000s to the early 1100s AD, although the buildings continued in use until around 1200. About 75% of those buildings were simple rectangular structures; the others were political-religious buildings such as t-shaped medicine lodges, square temples or council houses, circular buildings (rotundas and sweat baths) and rectangular shrine houses with deep basins.

Why Cahokia Blossomed

Cahokia's location within the American Bottom was crucial to its success. Within the limits of the floodplain are thousands of hectares of well-drained tillable land for farming, with abundant oxbow channels, marshes, and lakes that provided aquatic, terrestrial, and avian resources. Cahokia is also quite close to the rich prairie soils of the adjacent uplands where upland resources would have been available.

Cahokia's cosmopolitan center including people migrating in from different regions and access to a broad trading network from the gulf coast and southeast to the trans-Mississippi South. Vital trading partners included the Caddoans of the Arkansas River, people of the eastern plains, the upper Mississippi Valley, and the Great Lakes. Cahokians dabbled in long-distance trade of marine shell, shark teeth, pipestone, mica, Hixton quartzite, exotic cherts, copper, and galena.

Immigration and Cahokia's Rise and Fall

Recent scholarly research indicates that Cahokia's rise hinged on a massive wave of immigration, beginning in the decades before AD 1050. Evidence from upland villages in Greater Cahokia indicates that they were founded by immigrants from southeastern Missouri and southwestern Indiana.

The influx of immigrants has been discussed in the archaeological literature since the 1950s, but it was only recently that clear evidence showing a huge increase in population numbers was discovered. That evidence is in part the sheer number of residential buildings built during the Big Bang. That increase simply can't be accounted for by birth rates alone: there must have been an influx of people. Strontium stable isotope analysis by Slater and colleagues has revealed that fully one-third of the individuals in mortuary mounds at Cahokia's center were immigrants.

Many of the new immigrants moved to Cahokia during their late childhood or adolescence, and they came from multiple places of origin. One potential place is the Mississippian center of Aztalan in Wisconsin since strontium isotope ratios fall within that established for Aztalan.

Main Features: Monks Mound and Grand Plaza

Said to have been named after the monks who were using the mound in the 17th century, Monks Mound is the largest of the mounds at Cahokia, a quadrilateral flat-topped, earthen pyramid that supported a series of buildings on its upper level. It took about 720,000 cubic meters of earth to construct this 30 m (100 ft) tall, 320 m (1050 ft) north-south and 294 m (960 ft) east-west behemoth. Monk's Mound is slightly larger than Great Pyramid of Giza in Egypt, and 4/5 of the size of the Pyramid of the Sun at Teotihuacan.

Estimated at between 16-24 ha (40-60 ac) in area, the Grand Plaza just south of Monks Mound was marked by Round Top and Fox mounds on the south. A string of smaller mounds marks its east and west sides. Scholars believe it was first used as a source of soil for mound construction, but then it was purposefully leveled off, beginning at the end of the eleventh century. A wooden palisade enclosed the plaza during the Lohmann phase. It took an estimated labor of 10,000 person hours to build even 1/3-1/4 of the entire plaza, making it one of the largest construction projects at Cahokia.

Mound 72: The Beaded Burial

Mound 72 was a mortuary temple/charnel house, one of several used by the Mississippians at Cahokia. It is rather inconspicuous, measuring only 3 m (10.5 ft) high, 43 m (141 ft) long, 22 m (72 ft) wide, and it is located 860 m (.5 mi) south of Monks Mound. But it stands out because there were over 270 individuals deposited in 25 burial features (several suggesting human sacrifice), along with large votive caches of artifacts, including arrow bundles, mica deposits, discoidal "chunkey" stones, and masses of shell beads.

Up until recently, the primary burial at Mound 72 was considered a double burial of two men lying atop a beaded cloak with a bird's head, alongside several retainers. However, Emerson and colleagues (2016) recently restudied the discoveries from the mound including the skeletal materials. They found that, rather than being two men, the highest ranking individuals were a single male buried atop a single female. At least a dozen young men and women were buried as retainers. All but one of the retainer burials were either adolescents or young adults at the time of their deaths, but the central figures are both adults.

Between 12,000-20,000 marine shell beads were discovered intermingled with the skeletal material, but they were not in a single "cloak", but rather strings of beads and loose beads placed in and around the bodies. The researchers report that the "bird's head" shape shown in the illustrations from the original excavations may have been an intended image or simply fortuitous.

Mound 34 and Woodhenges

Mound 34 at Cahokia was occupied during the Moorehead phase of the site, and while it is neither the largest or most impressive of mounds, it held evidence of a copper workshop, a nearly unique set of data on the hammered copper process used by the Mississippians. Metal smelting was not known in North America at this time, but copper working, consisting of a combination of hammering and annealing, was part of the techniques.

Eight pieces of copper were retrieved from Mound 34 backfill, sheet copper covered in black and green corrosion product. All of the pieces are abandoned blanks or scraps, not the finished product. Chastain and colleagues examined the copper and ran experimental replications, and concluded that the process involved the reduction of large chunks of native copper into thin sheets by alternately hammering and annealing the metal, exposing it to an open wood fire for a few minutes.

Four or perhaps five massive circles or arcs of large postholes called "Wood Henges" or "post circle monuments" were found in Tract 51; another has been found near Mound 72. These have been interpreted as solar calendars, marking the solstices and equinoxes and no doubt the focus of community rituals.

Cahokia's End

Cahokia's abandonment was rapid, and that has been attributed to a wide variety of things, including famine, disease, nutritional stress, climate change, environmental degradation, social unrest, and warfare. However, given the recent identification of such a large percentage of immigrants in the population, researchers are suggesting an entirely new reason: unrest arising from diversity.

Americanist scholars argue that the city broke apart because the heterogeneous, multiethnic, likely polyglot society brought social and political competition between centralized and corporate leadership. There may have been kin-based and ethnic factionalism that may have reemerged after the Big Bang to splinter what began as ideological and political solidarity.

The highest population levels only lasted about two generations at Cahokia, and researchers suggest widespread and tumultuous political disorder sent groups of immigrants back out of the city. In what is an ironic twist for those of us who have long thought of Cahokia as the engine of change, it may well have been the people who abandoned Cahokia beginning in the mid-12th century that spread the Mississippian culture far and wide.