Meet Me By the Old Mounds

Over the course of our phone call, I congratulate Dr. Brooks Ellwood on his recent discovery. “I mean, the oldest manmade structure in North America!”

“Oldest known,” he corrected me.

These conversational speed bumps are not uncommon between geophysicists and English majors. I want to dream of the people who shaped the LSU mounds, eleven thousand years ago, we’re learning—and he needs to remind me that my imagination would be nowhere without thirty-one expensive carbon dates, high-powered microscopes, and a reverence for teeny-tiny relics. 

Ellwood did not use the phrase “teeny-tiny” or even “eensy-weensy” but spoke of phytoliths, highly durable microscopic particles found between plant cells, and osteons, the building blocks of mammals. It was a thick layer of ash seen in Mound A, the northern mound, that ignited this current investigation. The ash came from a fire so hot that it burned off the plants from which the phytoliths came. “You would never cook with reed and cane plants because the fire would be too hot and would destroy the meat you were interested in eating,” said Ellwood.

Ellwood’s wife, Sue, a member of his research team, found the osteons in the mound. The team, which also included an astronomer and a palynologist (a scientist who studies pollen and spores)  among other researchers, was able to use carbon-14 dating to trace the phytoliths and osteons back to 11,000 BP (before present). Human presence in North America dates back at least twice as long, to 22,000 BP, and it’s accepted that people made their way to Louisiana by 12,000 BP. (One must surmise they were stuck in gameday traffic.)

There are more than 800 mounds in Louisiana, including the Poverty Point complex and the Watson Brake mounds, located south of Monroe. Mounds had unique purposes to their builders: they could be used to improve a hunter’s line of sight, to bury the dead, to feast, to pray, or even just to live above the water. Here, the scathing fires and mammal bones point to a ceremony or a cremation.

The people who built the LSU mounds lived on the banks of what was then the Mississippi River Valley Estuary. The mounds were atop a terrace above the shore, and each mound is made from different materials and was built in phases, with some thousand years in between during which people may have vacated the area entirely during a climate event. Mound A contains much more water in its core and has shifted over time, helped along by less ancient rituals. “LSU students used to stand on the mounds during the game and jump up and down when the Tigers scored,” Ellwood noted. Mound B is more similar to the loess terrace on which it was built. A depression in the earth near Hill Memorial Library seems a likely source for the material.

The LSU Campus Mounds have been on the National Register of Historic Places since 1999, and Ellwood’s study—published in the American Journal of Science in August 2022—has done even more to spur their protection. “LSU now recognizes the significance of these mounds,” said Ellwood. “They’re working hard to protect them, looking for ways to put on ground cover that won’t damage the mounds.”

In the study, astronomer Geoffrey Clayton noted the alignment of the mounds would have provided prime viewing of the bright star Arcturus. Let’s thank that star and others for the interventions of Ellwood and his team. In 1967, our state saw fit to build a highway and demolish the Monte Sano mounds, fourteen miles north of the LSU mounds and once thought the oldest manmade structures themselves. “All these are archaeological sites,” said Ellwood. “We’re working to preserve them.”