Collinsville, Illinois, United States
Cahokia
About AD 1050 to 1150 at its height (Mississippian city)
A grass hill opposite St. Louis is a platform big enough to hold a building on top, and it is only the centre of a city of mounds. A ring of posts nearby is said to have watched the sun. The city itself was largely gone by about 1400, and the count of its people still moves when you change the rules.
Why this is extraordinary
Stand in the grass east of St. Louis and the ground rises in front of you like a hill that someone planned. That is Monks Mound, the great platform of Cahokia. The World Heritage listing calls it the largest prehistoric earthwork in the Americas, about 30 metres high, covering about six hectares, raised in four terraces and fourteen stages of basket-loads. Around it the city once held about 120 mounds, houses, and a stockade, spread over nearly 1,600 hectares. People farmed maize. The busy centuries fall between about 1050 and 1150, inside a longer Mississippian life from about 800 to 1400.
So how many people? The same listing offers 10,000 to 20,000 at that peak, a size that would have matched plenty of European towns of the day. Count the neighbouring mound towns across the river as one greater Cahokia and a Park Service account goes to 40,000 or 50,000. The catch is that a population is a reading of house floors, not a census. A house used in summer and a house lived in all year do not count the same, and the floors do not all survive.
East of the great mound, a circle of wooden posts once stood in the plaza. The wood is gone. What you can walk among now are new posts set where the holes were found, and the park reads them as a Woodhenge lined up with the sun through the year. A circle with many posts will catch a sunrise somewhere. The question is whether the builders chose the holes for the solstices and the equinox, or whether we are the ones drawing the lines. By about 1400 the plazas were quiet. Why a city that large emptied is the part no mound has answered.
Mound 72 is part of that quiet. A 2016 restudy finds the central beaded pair male and female, not two male warrior-chiefs, and reads that feature as renewal and fertility. Separate mass graves remain, one read as likely sacrifice and a later one, with trauma, as possible political violence. Sex corrects the 1960s map. It does not erase a hierarchy.
Oxygen isotopes in the oxbow beside the city are read, in a 2021 study, as drought from about 1200 to 1400 CE, with abandonment inside that span. An earlier reading of the same lake treats a shift in the isotopes as mixed seasonal rain, with a flood near 1150. One lake is not a failed field. Osage and Omaha texts have been set beside the figurines, the mound, and the posts. Those matches are analogies across centuries, not a dated transmission.
Why it matters
If Cahokia held tens of thousands, the Mississippian world had a true city north of Mexico, with the labour and the calendar to match. If the count is a few busy seasons stretched into a year-round census, the monument is no smaller, but the story of a metropolis is. The emptying matters either way. A place this built does not fade without a reason, and the reasons on offer do not yet agree.
Mississippian, here, is the farming culture of the river valleys in these centuries, with platform mounds, maize, and shell-tempered pottery. A platform mound is a flat-topped earthwork meant to hold a building, not a grave cone, though Cahokia has burial mounds too. Woodhenge is the modern name for the timber circle. The posts you see are replacements. The original red cedar is long gone.
Photo tour
2 photographs, unedited. On a phone, swipe the row. Choose one to look closely.
What is still unexplained
These sit beside the consensus account, with the same visual weight. None of them is marked solved.
Location and dating
- Location
- Cahokia Mounds State Historic Site, Collinsville, Illinois, east of the Mississippi and of St. Louis. Monks Mound is the great platform. The reconstructed timber circle stands to its west.
- Period label
- Current consensus — open to revision A Mississippian centre from about 800 to 1400, with the crowded years about 1050 to 1150. The timber circle belongs to that same florescence. The stairs and the new posts are ours.
- How this dating was done
- Pottery, house styles, and radiocarbon on the occupation, as gathered in the World Heritage account. The sun lines are archaeoastronomy of postholes. A new post does not date itself. The hole does, if charcoal or the sequence of circles can be tied to it.
- What could change it
- A house-by-house count that says how many roofs were up in one season, not across a century. Or a sunrise watched from a specified circle, with the holes that miss the sun written down beside the ones that catch it.
What is actually there
- Monks Mound is about 30 metres high and about six hectares at the base, in four terraces.
- The wider site once held about 120 mounds across nearly 1,600 hectares.
- Population figures run from 10,000–20,000 for the centre to 40,000–50,000 if neighbouring towns are included.
- A timber circle is read as aligned with the sun. The posts now standing are modern.
- The centre was largely empty by about 1400.
Open questions
| Question | Status |
|---|---|
| Was the timber circle a calendar, or a ring that happens to frame a sunrise? | Open. The park reads it as an observatory. A circle gives the sun several posts to rise behind. |
| Why did the city empty? | Open. A stockade, a climate shift, and a crowded floodplain are all still on the table. A flood-from-deforestation reading did not find the flood layers. |
The current narrative
Where publication stands today. It is the best-supported reading, and it is open to revision. It is not a verdict.
The current narrative — open to revision
A Mississippian city, with a solar circle
Cahokia was the great Mississippian centre north of Mexico, busiest between about 1050 and 1150, with on the order of 10,000 to 20,000 people and a timber circle used to watch the sun. It was largely abandoned by about 1400.
What supports this
- Monks Mound, about 120 other mounds, and a planned plaza, in the World Heritage description.
- The population range of 10,000 to 20,000 for the peak, and the longer span from about 800 to 1400.
- Post circles the park reads as aligned with the sun through the year.
- A stockade, rebuilt, around the core.
What pushes back
- Adding the neighbouring towns doubles the crowd, so the number is a boundary you draw.
- House counts can turn seasonal visits into a year-round city.
- A reconstructed circle can be aimed at a sunrise after the fact. The original posts are gone.
What would settle it
The city and the dates hold. The exact headcount and the exact purpose of the posts are the soft edges, not the mound.
Emerging narratives
Other published readings. Each may be right. None is adopted here unless the evidence carries it.
An emerging narrative
A ceremonial gathering place, not a metropolis
The mounds are real and huge, but the population figures treat a place of seasonal ceremony as if everyone slept there every night. The timber circle is a monument in the round, and the solar lines are our overlay.
What supports this
- Population totals swing from the teens of thousands to the forties once the map is widened.
- Many posts in a circle make an accidental sunrise cheap.
- Platform mounds across the Mississippian world often hold a temple or a chief's house, not a dense street of neighbours.
What pushes back
- The listing describes residential areas, not only ceremony, and a stockade around a lived core.
- Borrow pits and fourteen building stages are a lot of labour for a crowd that went home every autumn.
- The park's equinox line can be checked. It is not only a story.
What would settle it
A useful caution about the headcount. It does not shrink the earthwork, and it has to explain the houses.
Should the current view be reevaluated?
Consensus holds well
Cahokia is a Mississippian city centred on Monks Mound, fullest between about 1050 and 1150 and quiet by about 1400. The population is a range because houses are not a census. The timber circle is a real set of holes with a solar reading that a visitor can weigh in person, and should not treat as proved by the new wood alone.
What drives this
- A platform about 30 metres high and a field of about 120 mounds.
- A published population of about 10,000 to 20,000, and a larger figure if the neighbours are included.
- A timber circle read as a sun marker, now reconstructed.
- An emptying by about 1400 whose cause is still argued.
This is the museum’s own weighing of the evidence. It is not a visitor vote, and it is separate from the slider.
Weigh it yourself
Anonymous. Nothing here is stored except on this browser. Your lean does not change the assessment beside it.
Visitor lean so far — not evidence. On this browser only; a shared tally is not collected.
If the contested reading is right
What would follow if a reading that is not the consensus turned out to be true, and what could settle it. This explains the stakes. It does not adopt the reading.
The solar lines were planned
The plaza kept a calendar in cedar, and the posts were a public instrument, not only a ring. The several rebuildings would be maintenance of that instrument.
Why it is still worth a test
The sequence of circles dated, and a list of which holes meet a solstice or an equinox and which do not.
The crowd was seasonal
The monument stays. The word city gets quieter, and the labour has to be explained as gatherings rather than as a year-round town. The stockade still needs a reason.
Why it is still worth a test
Floors and food remains that show who was here in winter.
Sources
- Cahokia Mounds State Historic Site UNESCO World Heritage Centre
- Cahokia Mounds, a World Heritage Site National Park Service
- Evaluating narratives of ecocide with the stratigraphic record at Cahokia Geoarchaeology
- The beaded burial in Mound 72, a restudy American Antiquity, 2016. The central beaded pair read as male and female, and the feature as renewal and fertility. Mass graves remain.
- Drought in the oxbow beside Cahokia Scientific Reports, 2021. Oxygen isotopes read as drought from about 1200 to 1400 CE, with abandonment inside that span.
- Seasonal rain and a flood in the same lake PNAS, 2019. An earlier reading of the oxbow isotopes as a shift in seasonal rain, with flooding near 1150. One lake is not a failed field.
- Osage and Omaha texts beside Cahokia In Ancient Objects and Sacred Realms, University of Texas Press, 2007. Osage and Omaha texts set beside the figurines, Mound 72, and the posts. Analogies across centuries, not a dated transmission.
Image credits
- Monks Mound from the plaza. The stairs are modern. The earth is the monument, about 30 metres high in the World Heritage account, built in terraces.. Skubasteve834, CC BY-SA 3.0. Shown unedited.
- The reconstructed circle, with the centre post in front and Monks Mound beyond. These posts are modern, set in the old holes. The file's own caption treats this line as the equinox. That is the claim, standing in the grass.. QuartierLatin1968, CC BY-SA 3.0. Shown unedited.