The earthen works at Poverty Point have been described as one of the world's greatest feats of construction by an archaic civilization of hunters and gatherers, and have been nominated for recognition on the UNESCO World Heritage List that includes such famous cultural sites as the Taj Mahal, Machu Picchu and Stonehenge.
"What's extraordinary about these findings is that it provides some of the first evidence that early American hunter-gatherers were not as simplistic as we've tended to imagine," said study co-author T.R. Kidder, an anthropology professor at Washington University in St. Louis.
The researchers analyzed how one of the massive earth constructions, known as Mound, A was constructed about 3,200 years ago along a Mississippi River bayou in northeastern Louisiana.
"Our findings go against what has long been considered the academic consensus on hunter-gather societies -- that they lack the political organization necessary to bring together so many people to complete a labor-intensive project in such a short period," Kidder said in a university release.
Mound A had to have been built in a very short period because an exhaustive examination reveals no signs of rainfall or erosion during its construction, the researchers said.
"We're talking about an area of northern Louisiana that now tends to receive a great deal of rainfall," Kidder said. "Even in a very dry year, it would seem very unlikely that this location could go more than 90 days without experiencing some significant level of rainfall. Yet, the soil in these mounds shows no sign of erosion taking place during the construction period."
To complete such a construction within 90 days would have required the full attention of about 3,000 laborers, the researchers estimate.