Cahokia

Fourteen stages of earth

formationDrafted from Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989)

No chronicle names the people who built Cahokia or the leaders who directed them; nothing of the city's own language survives in writing. What survives instead is dirt, and archaeologists have learned to read it. Solid-core drilling through the site's central earthwork, the vast platform known today as Monks Mound, cut nine holes deep into its layers and found bands of limestone-rich soil and buried surfaces marking distinct episodes of construction - roughly fourteen of them in all.

Eighteen years to a layer

Radiocarbon dates recovered from material bracketing the mound's growth cluster between about A.D. 900 and 1150, a span of two and a half centuries into which the fourteen building stages fit at an average of some eighteen years apiece - each one, presumably, a distinct campaign of labor rather than a single continuous effort. Investigators who tried to estimate the workforce such a project would have required put the figure at around ten thousand people, an early sign of just how large a population the site was already drawing to itself.

The largest earthwork north of Mexico

By the time the mound reached its final form, its base covered roughly sixteen acres and its summit stood close to a hundred feet above the surrounding floodplain - the largest earthen monument built anywhere north of central Mexico, raised entirely by people who had no draft animals, no wheeled transport, and no metal tools to move the soil with. Whatever else Cahokia would become, its central mound alone was already, by the mid-twelfth century, a statement of organized labor on a scale nothing else in the region approached.

Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989) · Skubasteve834 · CC BY 4.0

A wall and a calendar

peakDrafted from Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989)

Nearly half of all the radiocarbon dates ever recovered from Cahokia - forty-five of ninety-five assays - fall between A.D. 950 and 1150, and a full quarter of them cluster even more tightly in the single century between 1050 and 1150. Whatever this settlement had been earlier, that century is when it was at its most crowded and its most active, and the population estimates for the site at its height, however debated among archaeologists, are not disputed in their general order of magnitude: more than ten thousand people, and by some reckonings as many as thirty thousand

• the largest and most densely settled community anywhere within the present-day United States before European contact.

A wall around the center

Sometime after A.D. 1100, in the later part of this same peak century, a large wooden palisade was raised enclosing roughly eighty-three hectares around the site's central plaza and its grandest mounds. Excavation shows the wall was deliberately taken down rather than left to rot where it stood, and later replacements of it extended construction into the thirteenth century. Whatever its purpose - excavators have doubted it was primarily defensive - it drew a clear line between an inner precinct of elite residences and mortuary buildings and the smaller mound-and-plaza clusters spreading out beyond it, home to lesser chiefs and to newcomers drawn from distant regions by Cahokia's own prosperity.

Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989) · Herb Roe · CC BY-SA 3.0

Circles of posts

Nearby, excavators found the remains of large circles built from rows of substantial wooden posts, later dubbed "Woodhenges" by the archaeologist who first mapped them. He read them as calendrical structures, aligned to track the solar year - a plausible enough reading, given how precisely Cahokia's own builders had already shown they could lay out an earthwork like Monks Mound on such a scale, that a community capable of moving that much earth might just as readily have wanted a way to track the turning of the seasons above it.

Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989) · QuartierLatin1968 · CC BY-SA 3.0

No one left to ask

endDrafted from Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989)

Cahokia's decline, like its rise, left no chronicle - only a thinning record in the ground. The radiocarbon evidence that clusters so heavily around the peak century of 1050 to 1150 falls away steadily in the assays dated afterward, and the site's own archaeological periodization places the whole Mississippian period - the era of Cahokia's mounds, plazas and palisade - between about A.D. 1000 and 1400. By the close of that span, the organized, densely populated center that had once required a wooden calendar and a wall around its own heart had ceased to function as one.

A name borrowed from elsewhere

When the first known European map of the area was drawn in 1796, it showed no mounds at all directly across from the site of St. Louis, and the district appears to have lain off the beaten track of the roads and river routes then in use. The name "Cahokia" itself was borrowed from an unrelated group living nearby in the historic era, part of the Illinois Confederation; there is no evidence they were themselves descended from, or connected to, the people who had raised the mounds centuries before. Whatever society had organized the labor of ten thousand people to build a hundred-foot pyramid and a solar calendar of wooden posts had, by the time any written record reached the region, already passed beyond memory - leaving only the earthwork itself to answer for it.

Fowler, The Cahokia Atlas: A Historical Atlas of Cahokia Archaeology (1989) · W. R. Brink & Co. · Public domain