For hundreds of years, Cahokia was home to the current state of Illinois. The bustling, vibrant city was once home to about 15,000 people, but was abandoned by the end of the 14th century – and researchers are still unsure why.
A study published last year was at least able to rule out one previous idea – that deforestation and overuse of the land around Cahokia caused excessive erosion and local flooding in the area, making it less inhabitable for Native Americans.
By analyzing sediment cores collected near earthen mounds at the state-owned Kahokia Mongs State Historic Site, researchers found that the country remained stable from Cahokia’s heyday to the mid-1800s and industrial development.
In other words, there was no environmental disaster.
“There’s a really common narrative about land use practices that lead to erosion and sedimentation and contribute to all of these environmental consequences,” said geoarchaeologist Caitlin Rankin from the University of Illinois at Urbana-Champaign at the time.
“When we actually revisit this, we’re not seeing evidence of the flooding.”
The mounds next to the excavation site are in low areas and close to a stream – a great position for any local flooding that might occur. However, there were no signs of sediment left over from the floods in the country.
It’s clear that the people who lived in Cahokia cut down a lot of trees, most probably to make defensive fortifications. However, the research, published in the journal Geoarchaeology in 2021, showed that this didn’t lead to the sort of erosion and flooding that would drive people from their homes.
“In this case, there was evidence of heavy wood use,” said Rankin in a press statement at the time. “But that doesn’t factor in the fact that people can reuse materials – much as you might recycle.”
“We should not automatically assume that deforestation was happening, or that deforestation caused this event.”
Cahokia remains a fascinating topic for experts, with a study published in 2020 analyzing ancient human feces to suggest that people began returning to Cahokia in significant numbers long before 16th-century European settlers began arriving. It is possible that leaving the metropolis did not actually last that long.
The mess we’re making of looking after the planet at the moment makes it easier to imagine ecocide being responsible for some of the unexplained mysteries of the past, the team behind the 2021 study says – but it’s important to keep digging to find the hard evidence as to what has actually happened.
“By eliminating this possibility, it moves us toward other explanations and requires we pursue other avenues of research,” said anthropologist Tristram Kidder from Washington University in St. Louis.