Cahokia is abandoned

Cahokia’s decline began long before its end. Around 1160–1170 a walled residential compound in its East St. Louis precinct was burned; about 1175 a palisade was first built around the city’s core, and it was later rebuilt several times to enclose ever smaller areas, as people left in growing numbers — by the middle of the 13th century the population had fallen by half or more. In the Moorehead phase (1200–1300) the old ritual buildings were given up, many mounds were capped and no longer enlarged, and the central authority seems to have weakened. By about 1350 the city was abandoned; some put its end as early as about 1300, others as late as about 1400.

The causes are still debated. Sediments of nearby Horseshoe Lake record major floods, and a study of fecal stanols — a chemical trace of human waste — found that a Mississippi flood and a shift to drier summers around 1150 coincided with the beginning of the decline. Other explanations include exhausted soils (a view some scholars dispute), health problems from a diet of maize that from about 1200 was no longer nixtamalized (cooked with an alkali), disease, warfare — in the 13th century palisades spread across the Midwest, and villages in the Illinois valley to the north were burned — and, as Thomas Emerson and Kristin Hedman argue, the fragmentation of a population with a large share of immigrants. Dhegiha Sioux peoples are thought to have been among those who left: Ponca oral tradition remembers the time of their ancestors at the city, which it calls P’ahé’žíde, the ‘red hill’.

Cahokia’s abandonment was part of the depopulation of a wide region — southern Illinois, western Kentucky and Tennessee and neighbouring lands — that archaeologists call the Vacant Quarter and once believed to have stayed empty from 1400 to 1600. A 2020 study of the Horseshoe Lake sediments found that the population of the area reached its lowest point around 1400 but had rebounded by about 1500; in the 17th century Illinois peoples, among them the Cahokia, who gave the site its name, moved into the region.