Cahokia’s ‘Big Bang’: a city rises on the Mississippi

Late Woodland farmers settled at Cahokia, on the American Bottom near the confluence of the Mississippi, Missouri and Illinois rivers, around 600. By the end of the 10th century small villages there were merging into larger communities, the first stage of Monks Mound had been begun, and maize, introduced around 900, had joined older native crops. Around 1050 change came abruptly: three urban precincts were built, an ordered grid oriented to the north was imposed on the earlier settlements, the Grand Plaza — some 20 hectares, deliberately levelled and filled — was laid out south of Monks Mound, and pottery and house styles across the region became uniform. Cahokia had been home to about 1,000 people before 1050; one study estimates that the population of its central area alone rose from 1,400–2,800 to 10,200–15,300 between 1050 and 1100, and estimates for the whole city at its peak range from 6,000 to 40,000.

The growth was fed by immigration: pottery from the lower Ohio, the lower Mississippi, the upper Midwest and the southern plains appears at the onset of the Big Bang, and many newcomers settled in farming villages in the uplands to the east. The pairing of a mound with a plaza was adopted from the Coles Creek culture of the lower Mississippi. Monks Mound, largely completed around 1100 after several building stages, rose 30 m on a base comparable to that of the Great Pyramid of Giza and carried a building more than 30 m long. In Mound 72 archaeologists found an elite burial on a bed of some 10,000 shell beads, among the remains of about 270 people, most of whom (about 62%) are thought to have been sacrificial victims.

Cahokia's contacts reached from the Great Lakes to the Gulf Coast: hoes of Mill Creek chert from southern Illinois, whose distribution Cahokia loosely controlled, were in demand among farmers, and Cahokians founded outposts as far away as Wisconsin and Mississippi. Its rise coincided, as the historian Daniel Richter notes, with that of the Chaco society in the Southwest, and the archaeologist Timothy Pauketat has suggested that the supernova of 1054 may have inspired its builders — a speculative idea for which there is no direct evidence. The city reached its height in the 12th century and was abandoned by about 1350; its mounds are a UNESCO World Heritage Site.