Cahokia

Cahokia is the largest thing pre-Columbian North America built, and one of the least explained. For a few centuries it was bigger than London.

The rise. Something happened around 1050 that archaeologists call the "big bang": a scattered farming population was rapidly reorganised into a planned city with a grand plaza, aligned mounds and a rebuilt landscape. It was deliberate and fast, and it implies an authority able to command labour on an enormous scale. Monks Mound alone required tens of millions of basket-loads of earth carried by hand.

Mound 72. The most-discussed excavation uncovered a sequence of burials that speak to that authority. A high-status individual was laid on a platform of more than twenty thousand marine-shell beads, with other rich burials nearby, and separate pits held the bodies of dozens of young women, and of men who appear to have been executed. It is the clearest evidence of social hierarchy and of human sacrifice north of Mexico, and it is read carefully: the ideology that made sense of it is gone, and cannot be reconstructed from the bones.

The emptying. By about 1350 the city was effectively abandoned, before any European saw it. No single cause has won out: overhunting and deforestation of the floodplain, flooding, drought, internal political failure and out-migration have all been argued, and several may have acted together. What is not in doubt is that this was not a mysterious disappearance of a people but a dispersal: the descendants moved, and their nations exist. The name "Cahokia" is itself a later borrowing, from an Illinois-confederacy group who happened to live nearby when the French arrived, centuries after the mound builders had gone.

Cahokia's largest mound is the biggest earthwork built in pre-Columbian North America, and one burial found within the site's mound complex points to organised human sacrifice on a scale rarely documented so clearly at any other Indigenous North American site.

The largest mound north of Mexico

Monks Mound, the central earthwork at Cahokia, covers a footprint larger than the base of the Great Pyramid of Giza and was built up in stages using an enormous volume of hand-carried earth, supporting what was likely an elite residence or ceremonial structure at its summit, a scale of engineered construction unmatched at any other known site north of Mesoamerica.

A calendar made of posts

Woodhenge, a series of large wooden post circles rebuilt several times at different diameters, functioned as a solar calendar, with specific posts aligned to mark sunrise positions at the solstices and equinoxes, evidence of precise astronomical observation built directly into the city's ceremonial landscape rather than left to informal seasonal tracking.

What Mound 72 held

Excavation of Mound 72 uncovered a man buried on a bed of thousands of shell beads, accompanied by the remains of numerous other individuals, including a group of young women, interpreted by archaeologists as retainer sacrifices accompanying an elite burial, among the clearest documented evidence of organised human sacrifice at any pre-Columbian site in eastern North America.