The Two Hills at LSU
What’s actually being argued about, and why nobody can settle it
There are two grass-covered mounds on the Louisiana State University campus in Baton Rouge, standing on the edge of a loess bluff above the Mississippi floodplain. Mound A to the north, Mound B to the south. Both about seventeen feet high, both a little over a hundred and twenty feet across at the base. If you didn’t know, you’d walk past them.
For most of a century, people did more than walk past them. They ran up them, biked on them, sat on them, slid down them, and tailgated on them before games. The university has since put in barriers, signage, and game-day rules to stop it.
The first written mention of them is from 1851, in an article in De Bow’s Review noting American Indian mounds on the McHatton Plantation south of Baton Rouge. The land became LSU’s campus in the 1920s. No professional archaeologist examined the mounds until 1982.
That’s a hundred and thirty years of people knowing exactly where they were, and nobody asking the obvious question.
The number that started the fight
In 2022, a team led by LSU geologist Brooks Ellwood published a paper in the American Journal of Science with a title that left no room for hedging: the LSU Campus Mounds, with construction beginning around eleven thousand years ago, are the oldest known extant man-made structures in the Americas.
Eleven thousand years. That’s within a few centuries of the end of the Pleistocene. It would mean people were raising monumental earthworks in Louisiana while there was still ice sitting on Canada.
It would also make these two hills older than every structure most people can name. Older than Stonehenge by roughly six thousand years. Older than the Great Pyramid by more than six thousand. Older than the oldest known writing anywhere on earth.
Then LSU’s own archaeologists published a response saying the mounds are probably five to seven thousand years old.
Same university. Different buildings. Both peer-reviewed.
Why they disagree and this is the part worth understanding
Here’s what most coverage got wrong, including some that should have known better. The archaeologists are not saying the dates are fake. They said so explicitly: they do not dispute the accuracy of the data or the radiocarbon results themselves.
They also went out of their way to say they aren’t rejecting it because it’s too old. That matters, because that reflex has a bad history in American archaeology. For a long time the field operated on a model that said monument-building required farming, and therefore hunter-gatherers couldn’t have built mounds. That model is dead. Sites across the Gulf and lower Atlantic coasts and up into the Green River valley in Kentucky have established that mound-building by fisher-hunter-gatherers goes back at least seven thousand years. Nobody serious argues otherwise anymore.
So the objection isn’t the number. It’s what was dated.
Ellwood’s team dated organic material found inside the mound fill, ash from burned reed and cane, and burned mammal bone, recovered from sediment cores.
Now think about what a mound actually is. It’s dirt that somebody dug up somewhere and carried somewhere else. And the dirt they dug up already had things in it.
If you scoop up soil that happens to contain charcoal from a natural fire that burned three thousand years before you were born, and you carry that soil up a hill and pile it into a mound, then a scientist coring that mound five thousand years later will find charcoal that dates to eight thousand years ago sitting inside a structure that’s five thousand years old.
The carbon date is more than likely correct. The date of the mound is not.
Archaeologists call this the inherited age problem, and it’s one of the oldest traps in the discipline. Radiocarbon tells you when an organism died. It does not tell you when a human being moved the dirt that organism was buried in.
The rebuttal’s specific objection is that Ellwood’s team dated natural sediment inclusions rather than material securely tied to construction and that earlier sediment dates from the base of Mound A, taken by Robert Neuman in the 1980s, came back around six thousand years and give good reason for caution.
The test that could settle it
Chip McGimsey, who spent three decades as Louisiana’s state archaeologist, has been pushing for a different method entirely: optically stimulated luminescence, or OSL.
OSL doesn’t date organic material. It dates the mineral grains themselves, specifically, the last time those grains were exposed to sunlight. Bury a grain of quartz and it starts accumulating a measurable signal from background radiation. Expose it to light and the counter resets to zero.
Which means OSL doesn’t tell you how old the dirt is. It tells you when somebody buried it.
That’s exactly the question. That testing is underway now.
What came out of the cores
Set the argument aside for a moment, because both sides agree on what the cores contained, and it’s remarkable regardless of the date.
The cores came back in layers. Ash from burned reed and cane. Burned mammal bone. Then sterile fill. Then more ash, more bone. Repeating at different depths, separated by long stretches of time.
That is not what construction fill looks like. That’s a record of fire, set on the mound surface, repeatedly, then covered over and built higher, then set again.
Whatever these mounds were for, people came back to the top of them and burned things there, across a span of time long enough that the generations doing it could not have known each other.
The abandonment
There’s a second detail in Ellwood’s findings that got very little attention.
According to his reading of the cores, people stopped using the first mound around eighty-two hundred years ago. Then, roughly seven thousand five hundred years ago, they came back and started building a new one just to the north, this time hauling mud up from the floodplain below, from ground that today sits at the entrance to Tiger Stadium.
Ellwood’s own comment on the gap was that they don’t know why the mounds were abandoned, but that the environment changed suddenly and dramatically.
It’s worth knowing what sits at that date. Around eighty-two hundred years ago, the global climate underwent an abrupt cooling event, sharp, severe, and visible in ice cores in Greenland and sediment records worldwide. Climate scientists call it the 8.2 kiloyear event. It’s one of the best-documented sudden climate shifts of the entire Holocene.
I want to be careful here. Ellwood’s dating is the disputed dating, and correlation across an eight-thousand-year gap is not causation. But if his numbers hold, then the abandonment of the oldest monument in the Americas lines up with a global climate event that we can independently see in Greenland ice.
That’s either a coincidence or it isn’t. Both possibilities are interesting.
Who they were
Whichever date you take, these were not farmers.
At five to seven thousand years ago (the Middle Archaic in this region) the archaeological picture is of bands of roughly twenty to fifty people living off the land and moving seasonally to follow what was available. No agriculture. No pottery. No permanent year-round settlement.
And they built this anyway. Not once, repeatedly, in stages, with pauses of centuries between them, which means the intention survived across dozens of generations of people who never met.
That’s the part that should stay with you. Not the tonnage. The continuity. Somebody told somebody, who told somebody, who told somebody, for longer than recorded history has existed, and the message survived intact enough that they kept building.
Why Louisiana
None of this is isolated. Louisiana is arguably where monumental architecture in the Americas begins.
Watson Brake, in the northeast part of the state, has been dated to roughly fifty-four hundred years; eleven mounds in an oval, built by hunter-gatherers, predating the Egyptian pyramids. Poverty Point, a few hundred miles from there, is a UNESCO World Heritage Site.
The state has over eight hundred recorded mounds. Most have been destroyed.
The LSU pair are the oldest in Louisiana that the public can actually walk up to. That’s the whole reason they matter beyond the academic argument — almost every site of this significance is gone, fenced, or on private land.
What happens next
Mound A is in trouble.
The floodplain mud it was built from is still saturated. Saturated fine sediment liquefies when it’s agitated, it stops behaving like a solid and starts behaving like a fluid. So the mound is unstable and degrading, and every footfall on it accelerates that.
The barriers, the signage, and the game-day rules exist for that reason. If you go, stay off them. This is one of the few places left where you can stand near something this old in America, and it will not survive being climbed.
Two departments at the same university have been arguing for four years over how old these hills are. Meanwhile the hills are falling apart, and almost nobody outside Baton Rouge has heard of them.
Every conquered society gets its architecture reassigned. It happened here.
Ask yourself where else it’s happened.
There is a country buried underneath this one. And you’re standing on it right now.
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