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Aerial view of the earthen mounds of Cahokia, Illinois, across the Mississippi River from St. Louis, Missouri. A huge marker from Cahokia was cut 900 years ago and came from more than 100 miles away, a new study suggests. | Credit: Matt Champlin via Getty Images.
About 900 years ago, Native Americans at Cahokia — the largest pre-Columbian city north of pre-Colonial Mexico — cut down a giant tree and transported it more than 110 miles (180 kilometers) to serve as a monumental marker, a new study reveals.
The tree, known as the Mitchell Log, is the largest marker of its kind in Cahokia, now known for its earthen mounds in southwestern Illinois.
The marker posts were important monuments in Cahokia, but researchers are still not sure when the Cahokia people built and eventually stopped laying these large logs.
After establishing the exact dates of Mitchell’s journal placement and removal, the researchers of the new study published in the journal on October 3. PLOS Oneproduced the most accurate timeline yet of Cahokia’s rise to power and subsequent decline. Also, by determining where the marker post came from, researchers raise new questions about the transport of thousands of similar marker posts during the height of Cahokia’s influence.
A big city
Cahokia was home to up to 20,000 people, with a peak of between 1,050 and 1,200.
“Cahokia grew rapidly in the late 11th century immigrants, who make up as much as a third of the populationIn the mid-12th century, when Cahokian goods, people and ideas reached the Gulf Coast to the Great Plains,” the study’s first author said. Nicholas KesslerAssociate Research Professor at the Tree Ring Research Laboratory at the University of Arizona and co-author of the study Erin BensonAn Eastern Woodland archaeologist at the University of Illinois at Urbana-Champaign told Live Science in an email.
During this time, the Cahocians built large monumental structures called marker posts. These posts were carved from massive tree trunks and were usually placed near communal courtyards, on top of pyramidal mounds and prominent buildings.
“In the pre-contact Cahokian world, poles were often erected in special places (squares, mounds, temples) where they functioned as axis of the worldphysically connecting the upper, middle, and lower worlds and helping to mediate these powers and people’s relationships with them,” Kessler and Benson said.
However, by 1200 Cahokia’s political, social, and economic influence declined, and marker posts were no longer built.
In order to better understand the timeline and provenance of the Mitchell Log, the team radioactive carbon-dated the record and investigated its provenance. They did this by studying the ratios of strontium isotopes, which are atoms of the element strontium with different numbers of neutrons in their nuclei. Strontium occurs naturally in bedrock and has a unique isotopic signature depending on location. This signature acts like a fingerprint and is transmitted with slight variations to the water and the plants growing on it. By studying the signature of an animal or plant, scientists can determine which bedrock they came from.
Scientists determined that the once 59-foot (18-meter) and 4.4-5.5-ton (4-5 metric tons) log likely came from more than 110 miles from southern Illinois.
The Cahokia people likely transported the log by floating or rafting upstream, Kessler and Benson said. “Or they could have simply carried it overland via trails and roads that undoubtedly connected Cahokia to surrounding communities,” the authors said.
Using cosmic events archived in tree rings, the felling of the tree was dated to 1124, coinciding with the city’s heyday. These cosmic events are characterized by sudden jumps cosmic radiationespecially radioactive carbon, usually caused by solar storms or supernovae. Trees produce one tree ring each year, which stores radiocarbon, so these sharp spikes are recorded in their rings and can be used to pinpoint specific calendar years.
Assuming that the Mitchell Log stood for a generation or two before natural decay led to its removal, the marker post probably stood between 1150 and 1175. This period corresponds to the time when nearby ceremonial centers were abandoned after the decline of Cahokia, which provides more information about this event.
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In the second half of the 12th century, Cahokia underwent a variety of changes, including increased droughts, changes in the types of exotic goods traded, the transformation of public spaces and the construction of mounds, the researchers explained in their study.
Whether all of the Cahokia marker records were mined around this time remains a question the authors hope to answer in future research. In any case, the evidence shows that by 1200 No new markers were placed in Cahokia. Until 1400 the city was abandoned for reasons still unknown to archaeologists.