United States Medieval Built: c. 700–1400 AD UNESCO

Cahokia Mounds

Cahokia was the largest pre-Columbian city north of Mexico, a planned urban centre situated on the fertile floodplain of the Mississippi River near present-day Collinsville, Illinois, that at its peak around 1100 AD housed an estimated 10,000 to 20,000 people — making it larger than contemporary London. The city was built by the Mississippian culture and organised around a grid of open plazas flanked by more than 120 earthen mounds of varying sizes and functions, serving as platforms for temples, residences of elites, and burial tumuli. The centrepiece is Monks Mound, a four-terraced earthen pyramid covering 5.6 hectares at its base — larger in footprint than the Great Pyramid of Giza — and standing 30 metres tall, constructed entirely from more than 22 million cubic feet of hand-carried earth. Cahokia was mysteriously abandoned around 1350 AD, leaving no written records and no clear explanation, though archaeological evidence points to a combination of political instability, flooding, deforestation, and resource depletion.

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Cahokia Mounds

United States

Longitude: -90.062

Latitude: 38.6553

Historical Significance

Cahokia stands as the most sophisticated and largest urban complex in North American prehistory, demonstrating that complex, hierarchical, and densely populated civilisations developed independently north of Mexico centuries before European contact. Its UNESCO World Heritage designation recognises its exceptional testimony to the Mississippian culture's urban planning, ceremonial architecture, and far-reaching trade networks that connected communities from the Gulf Coast to the Great Lakes.

Facts

Fact 1

Monks Mound's Staggering Scale

Monks Mound covers 5.6 hectares at its base — larger than the footprint of the Great Pyramid of Giza — and was constructed entirely without metal tools or draft animals by workers carrying earth in baskets, one load at a time over several centuries.

Fact 2

Woodhenge

Archaeologists have identified at least five large timber circles near Monks Mound, dubbed "Woodhenges," built from massive red cedar posts aligned to mark the solstices and equinoxes — demonstrating sophisticated astronomical knowledge among Cahokia's planners.

Fact 3

Beaded Burial of a King

In Mound 72, excavators found the burial of a high-status individual lying on a bed of 20,000 marine shell beads arranged in the shape of a falcon — accompanied by the mass graves of over 250 sacrificed individuals, mostly young women, in nearby pits.

Fact 4

City Larger Than Medieval London

At its peak around 1100 AD, Cahokia's population of up to 20,000 people made it larger than contemporary London and equal in size to many European capitals of the same era — a fact that challenges traditional narratives of pre-Columbian North America as sparsely populated.

Fact 5

A Planned City

Cahokia was not an organic settlement but a deliberately planned urban centre — its mounds, plazas, and residential areas were laid out according to a precise cardinal grid aligned to the sun, indicating centralised planning authority and sophisticated surveying techniques.

Fact 6

Mysterious Abandonment

By 1350 AD Cahokia was completely abandoned, leaving no written explanation — palaeoclimate data suggests catastrophic flooding of the Mississippi floodplain around 1150 AD triggered a population exodus, while evidence of wooden palisade walls suggests increasing warfare in the city's final decades.

See Also