We told you so! Smithsonian Magazine: A new study finds that enormous mounds and concentric earthen ridges were built in a matter of months.

New research shows that people who lived in what’s now north Louisiana around 3,400 years ago had sophisticated engineering expertise, David Nield reports for Science Alert. The remains of earthen mounds built by the mysterious civilization still rise as much as 66 feet above the ground at Poverty Point, Louisiana. The new study, published in the journal Southeastern Archaeology, finds that people of the region raised the enormous earthworks in a matter of months or even just weeks.

“One of the most remarkable things is that these earthworks have held together for more than 3,000 years with no failure or major erosion,” study author Tristram R. Kidder, an anthropologist at the University of Washington in St. Louis, says in a statement. “By comparison, modern bridges, highways and dams fail with amazing regularity because building things out of dirt is more complicated than you would think. They really were incredible engineers with very sophisticated technical knowledge.” Continue reading…