Cahokia

In Illinois today, on the east bank of the Mississippi, there is a hill beside a highway. Thirty metres high, four terraces, flat on top. It is not a natural hill; it is made entirely of earth carried there by hand.

This mound is the largest earthwork in the Americas north of Mexico. Its footprint is wider than that of the Great Pyramid at Giza. No wheel was used in building it and no draught animal: there were no horses and no oxen. The earth came in baskets — estimates run to more than fourteen million basket loads.

A City, Not An Empire

The ground around it is a field of mounds. More than a hundred are on record, and some have been flattened by farming and building. They are not scattered at random; they sit around a great plaza, aligned to a main axis. This is not a settlement but a planned city.

Its densest period falls roughly between 1050 and 1200. Population estimates vary, but the centre is usually given at ten to twenty thousand. That is comparable to London at the same date, and no other settlement in North America reached this size again until Philadelphia in the 1780s.

The people who made it belonged to a broad tradition called Mississippian: communities living on maize agriculture, trading along the rivers, building on top of mounds. Cahokia was the largest knot in that network.

The Circle Of Posts

West of the city, a circular arrangement of red cedar posts was found. When excavators uncovered the post holes, they saw that the circle had a separate observation post at its centre, and that some of the perimeter posts aligned with the sunrises of the solstices and equinoxes.

This is the same logic as at Newgrange or Stonehenge: fixing a particular day of the year by marking where the sun comes up on the horizon. The difference is the material — wood rather than stone — so the instrument itself rotted away and only its holes are left.

The City Whose Name We Do Not Know

The most striking thing here is neither its size nor its mounds. We do not know this city's real name.

The name Cahokia comes from a people who settled in the region long afterwards, centuries after the place was abandoned. That people has no direct connection to the mound builders. The name we use today, in other words, is not the name its builders gave it; it is a label that stuck through proximity.

The same holds for everything else. There was no writing here, so how these people named themselves, what language they spoke, what their rulers were called — none of it was recorded. We have a thirty-metre structure and not one word from the people who raised it.

One excavated burial shows a stratified society: an interment on some twenty thousand shell beads laid out in the shape of a bird, with many other burials beside it. That points to a class holding power and ceremony — and again, we do not know what that class called itself.

Today

The city largely emptied around 1350. Why is disputed: exhaustion of firewood and resources, flooding, climate shift, political collapse — all have been proposed, none proven on its own.

The site was inscribed on the UNESCO World Heritage list in 1982. The main conservation problem is modern development: a road runs through the site, part of it was formerly a housing subdivision and a drive-in cinema, and some of the surrounding mounds were levelled for farming. Earth structures also bring their own difficulty — rain cuts into the surface, and the slopes of the mounds have to be repaired on a regular cycle.