Drought Was Not The Reason Cahokia, North America’s First City Was Suddenly Abandoned – New Study
Jan Bartek - AncientPages.com - The Cahokia Mounds settlement near present-day St. Louis was a significant urban center approximately 900 years ago. With a metropolitan population of around 50,000, it ranked among the world's largest communities at that time. Cahokia was North America’s first city. However, by 1400, this once-thriving settlement had been largely abandoned, a phenomenon that continues to puzzle researchers.
Cahokia. Credit: Adobe Stock - Kent
A widely accepted hypothesis attributes the mass exodus to a severe crop failure resulting from an extended period of drought. However, recent research published in the journal The Holocene challenges this notion. The study, conducted by Natalie Mueller, an assistant professor of archaeology at Washington University in St. Louis, and Caitlin Rankin, Ph.D., suggests that the Cahokians likely had alternative motivations for departing the settlement.
This new research indicates that the reasons behind the abandonment of Cahokia may be more complex than previously thought, opening up new avenues for archaeological investigation and historical understanding of this ancient urban center.
The research conducted at the historic Cahokia site provides valuable insights into the environmental conditions during the period of population collapse. Dr. Rankin's study focused on analyzing carbon isotopes in soil samples to understand the plant life and climate of the era.
Carbon isotopes, specifically Carbon 12 and Carbon 13, are used by plants during photosynthesis. Different types of plants utilize these isotopes in varying ratios, which can be detected in soil samples long after the plants have decayed. This method allows researchers to determine the types of vegetation prevalent in a given area at a specific time.
Plants adapted to dry climates, such as prairie grasses and maize (an important crop during the Cahokia period), leave behind a distinct carbon signature. In contrast, other plants that were likely part of the Cahokian diet, including squash, goosefoot, and sumpweed, produce a carbon signature similar to that of wetland and forest plants.
The analysis of Dr. Rankin's soil samples revealed that the ratios of Carbon 12 and Carbon 13 remained relatively stable during the crucial period of population decline. This consistency suggests no significant change in the types of plants growing in the area during this time.
This information is particularly relevant because it contradicts the hypothesis that a dramatic shift in vegetation, possibly due to drought, may have contributed to the collapse of the Cahokian civilization. The stable carbon isotope ratios indicate that the local plant ecosystem did not undergo substantial changes, providing new perspectives on the factors that may have influenced the decline of this ancient society.
"We saw no evidence that prairie grasses were taking over, which we would expect in a scenario where widespread crop failure was occurring," Mueller said.
The Cahokians showcased advanced technological skills, including engineering and irrigation. These capabilities may have helped them maintain crop production during environmental challenges. Dr. Rankin suggests this could have protected them from severe drought impacts. The society also demonstrated sophisticated resource management, likely implementing food storage systems.
The remains of the most sophisticated prehistoric native civilization north of Mexico are preserved at Cahokia Mounds State Historic Site in Illinois. Archaeologist Natalie Mueller's new study casts doubt on a popular theory about why the ancient city was abandoned. Credit: Joe Angeles / Washington University
Their diverse diet included various proteins, fruits, and nuts, providing resilience against potential food shortages. Mueller is developing a database of paleo-botanical evidence to understand Midwestern Indigenous agricultural practices and diets better, potentially revealing insights into their adaptations.
"Gathering that information would help us see if people switched to different crops in response to climate change," she said. She's also planning to grow certain food crops in controlled conditions on campus to understand how they might have responded to ancient droughts and other challenges.
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So, why did the Cahokians leave their land of plenty? Mueller suspects it was a gradual process.
"I don't envision a scene where thousands of people were suddenly streaming out of town," she said. "People probably just spread out to be near kin or to find different opportunities."
"They put a lot of effort into building these mounds, but there were probably external pressures that caused them to leave," Rankin said. "The picture is likely complicated."
The study was published in the journal The Holocene
Written by Jan Bartek - AncientPages.com Staff Writer