SOCIETY × ENVIRONMENT

The Mounds of Cahokia

~1050 CE

History · Middle Ages · Holocene · Meghalayan

Around 1050 CE, on the Mississippi floodplain across from modern St. Louis, a planned city rose almost at once: earthen pyramids set around great plazas, drawing thousands of people and fed by fields of maize. The largest of them, Monks Mound, covers more ground at its base than the Great Pyramid of Giza. Cahokia flourished through a rare lull in the river's great floods; severe drought set in from 1150, the city walled itself in, and by 1200 it had lost half its people. The great floods returned after 1200, and by 1350 the region had fallen silent.

Why it matters

North America had its metropolis five centuries before Europeans reached the Mississippi, and its rise and fall are now read with the full toolkit: tree rings, flood sediments, even molecular traces of its inhabitants in lake mud. Cahokia belongs with the Maya and Angkor in the modern ledger of cities strained by climate, and it corrects a durable blind spot: the lands north of Mexico were never a wilderness waiting for history to begin.

Dating & uncertainty

Central Cahokia was built abruptly around 1050 CE, during one of the wettest half-centuries of the millennium. Decline set in from about 1150, amid drought and Mississippi flooding; a palisade of twenty thousand logs went up around Monks Mound and the Grand Plaza, read as a sign of unrest, and the region was abandoned by about 1350. A molecular census, faecal markers in lake sediments, now tracks the population rising and falling.

Sources

1. Muñoz et al. (2015), PNAS · Cahokia's emergence and decline coincided with shifts of flood frequency on the Mississippi Riverdoi:10.1073/pnas.1501904112
2. White et al. (2019), PNAS · Fecal stanols show simultaneous flooding and seasonal precipitation change correlate with Cahokia's population declinedoi:10.1073/pnas.1809400116
3. Benson, Pauketat & Cook (2009), American Antiquity · Cahokia's boom and bust in the context of climate changedoi:10.1017/s000273160004871x

Our species’ history as one day

23:55:324 min 28 s before midnight

if the 315,000 years of Homo sapiens were compressed into a single day