Cahokia was a city that, at its peak from A.D. 1050-1200, was larger than many European cities, including London. The city was spread out over six square miles (16 square kilometers) and encompassed at least 120 mounds and a population between 10,000 and 20,000 people.
Located across the Mississippi River from modern-day St. Louis, it was the largest pre-Columbian city north of Mexico. The inhabitants of Cahokia did not use a writing system, and researchers today rely heavily on archaeology to interpret it. The name "Cahokia" is from an aboriginal people who lived in the area during the 17th century.
Cultural finds from the city include evidence of a popular game called "Chunkey" and a caffeine loaded drink. Artistic finds include stone tablets carved with images (such as a birdman) as well as evidence of sophisticated copper working, including jewelry and headdresses.
Recent research shows that many of the people who lived at Cahokia were immigrants who came from across the Midwest, possibly traveling from as far away as the Great Lakes and Gulf Coast, a study of their teeth shows. To the south of Cahokia a settlement that archaeologists call Washausen became abandoned around the time Cahokia was at its peak around A.D. 1100, a study published recently in the Journal of Archaeological Science Reports found. It's possible that some of the residents at Washausen, and other sites located near it, moved to Cahokia.
The city's growth may have been aided by warmer temperatures. At the time Cahokia flourished, temperatures across the Earth were unusually warm, resulting in increased rainfall in the American Midwest, wrote archaeologists Timothy Pauketat and Susan Alt in a paper published in the book "Medieval Mississippians: The Cahokian World" (School for Advanced Research Press, 2015). "An increase in average yearly precipitation accompanied the warmer weather, permitting maize farming to thrive," Pauketat and Alt wrote.
The city fell into decline after 1200, around the time that a flood occurred, becoming abandoned by 1400. Much of the city lies buried under 19th- and 20th-century developments, including a highway and the growth of the city of St. Louis. Over the past few decades, efforts have been made to preserve what remains, with Cahokia's core now part of a state historic site.
The most awesome example of architecture at Cahokia is the 100-foot (30-meter) tall "Monks Mound" — the name given to it because a group of Trappist monks lived near it in historic times.
It was built with four terraces, covering about 17 acres (6.8 hectares) at its base, the mound towering over the city. Archaeologists have found giant postholes at the top indicating the presence of what may have been a temple, presumably made of wood, measuring 104 feet (31 m) by 48 feet (15 m). Its postholes are over 3 feet (1 m) in diameter, the building being perhaps 50 feet (15 m) tall.
Monks Mound, along with a grand plaza and a group of smaller mounds, was walled in with a 2-mile-long (3.2 km) wooden palisade. As many as 20,000 wooden posts were used to construct it.
To the west of Monks Mound is a series of five circles, each originally made of red cedar wood posts, constructed at different times between A.D. 900 and 1100. They vary in size from 12 to 60 posts, the latest one being the smallest. Archaeologists refer to these structures as a "woodhenge," a reconstruction of which now exists.
These posts would likely have been used as a calendar of sorts marking the solstices, equinoxes and festivals important to the inhabitants. A priest could have stood on a raised platform in the middle.
The sunrise during the equinox, when it rises to the east, is said to be particularly spectacular from this spot. A post aligns with the front of Monks Mound and the massive structure looks like it "gives birth" to the sun, according to a modern account recorded on the Cahokia Mounds state historic site website.
Mound 72 is a 10-foot-high (3 m) structure located less than a half-mile south of Monks Mound. It dates between 1050 and 1150 and holds the remains of 272 people, many of them sacrificed — the largest number of sacrificial victims ever found north of Mexico.
The mound's archaeology is complicated but several instances of human sacrifice can be made out. In one case, 39 men and women were executed "on the spot," wrote Pauketat in the book "Cahokia: Ancient America's Great City on the Mississippi" (Penguin, 2010). "It seemed likely the victims had been lined up on the edge of the pit ... and clubbed one by one so that their bodies fell sequentially into it."
In another episode of sacrifice, 52 malnourished women between the ages of 18 and 23 appear to have been sacrificed at the same time, along with a woman in her 30s. It's not known why these women were sacrificed. A study of the teeth of the women indicates that many of them are from the local area, suggesting that they were not captured during a war.
The burial mound also has the remains of a man and woman who were found buried with 20,000 shell beads, likely the remains of a garment(s). They may have been a couple that had a great amount of power at Cahokia. Near their remains archaeologists found the burials of 12 other people including several male-female couples as well as the remains of a child.
The absence of written records makes it difficult for researchers to understand all the religious and spiritual beliefs that the residents of Cahokia had. However, "new evidence suggests that the central Cahokia precinct was designed to align with calendrical and cosmological referents — sun, moon, earth, water and the netherworld," wrote a team of archaeologists in an article published in 2017 in the journal Antiquity.
For instance, there is a place that archaeologists call the "Emerald Acropolis," which marks "the beginning of a processional route" that leads to central Cahokia, the archaeologists wrote in the journal article. At least 12 mounds along with the remains of wooden buildings (some of which were likely used as "shrines") have been identified at this acropolis the archaeologists wrote, noting that the mounds and wooden buildings have "lunar alignments."
Additionally, water may have played a role in the rituals performed at the acropolis. Some of the buildings were ritually "closed" with "water-redeposited silts" put over them, the archaeologists wrote. In a few cases, mats or hides were burned inside the buildings before silt was put over them. A burial of an infant was found in one of the buildings and may have been placed inside as an "offering" archaeologists wrote.
Cahokia supported a rich variety of art and cultural activities. Among them are stones used for a once wildly popular game called "Chunkey."
Archaeologists cannot be certain what the exact rules were at the time Cahokia thrived. Accounts of the game in the 18th and 19th century tell of a stone disc, called a "chunkey stone," that would be rolled on a playing field with people throwing giant sticks, larger than themselves, at it, trying to land them as close to the stone as possible. Points would be given depending on how close they came. Gambling on the outcome of this game was common, according to writers who lived in the 18th and 19th centuries.
Pauketat envisions Chunkey being played as a team sport at Cahokia in the plaza beside Monks Mound. In an Archaeology Magazine article, he writes that "the chief standing at the summit of the black, packed-earth pyramid raises his arms. In the grand plaza below, a deafening shout erupts from 1,000 gathered souls. Then the crowd divides in two, and both groups run across the plaza, shrieking wildly. Hundreds of spears fly through the air toward a small rolling stone disk ..." Spectators would cheer them on, witnessing a great sport that captivated the North American city.
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Owen Jarus is a regular contributor to Live Science who writes about archaeology and humans' past. He has also written for The Independent (UK), The Canadian Press (CP) and The Associated Press (AP), among others. Owen has a bachelor of arts degree from the University of Toronto and a journalism degree from Ryerson University.