The earthworks at Poverty Point, Louisiana, are considered one of the most impressive construction feats of prehistoric North America. Two weeks ago, the site was nominated for inclusion on UNESCO's list of World Heritage sites, where it would join 21 other U.S. landmarks, including the Statue of Liberty and the Grand Canyon.
Little is known about the series of mounds and ridges or the hunter-gatherer society that created them, besides that they were built between three and four thousand years ago. The prevailing wisdom has been that their mass accumulated over hundreds of years.
But this week, researchers from Washington University in St. Louis and Murray State University announced that the largest of the mounds, "Mound A," which covers over 500,000 square feet, was built in fewer than 90 days.
By analyzing soil patterns, the researchers concluded that there had been no serious erosion during the construction of the mound, and thus no heavy rainfall. In a region as rainy as the American Southeast, this indicates a staggering speed of construction.
Why does this matter? For people without organized agriculture, permanent settlements, domesticated draft animals or sophisticated tools like wheelbarrows, moving over 300,000 square yards of dirt in so short a time -- about eight million basket loads -- would have required an unprecedented degree of political structure. (A modern dump truck would require over 10,000 loads to do the same.)
Hunter-gatherers are typically thought to have existed in small societies of dozens of people. Building Mound A in less than three months would have required, the study estimates, a gathering of 9,000 people.
Top image: Flickr user Kniemla. Inset: Creative Commons.