October 12, 2021
Researchers at Washington University, St. Louis have found that the inhabitants of Poverty Point in Louisiana 3,400 years ago were highly skilled engineers who could build massive earthen structures in months that lasted far into the future. Their earthworks have have held together for 3,000 years with no failure or erosion. They built 72 foot tall earthen mounds without modern tools, horses or wheels.
Using modern research methods: radiocarbon dating, microscopic analysis of soils and magnetic measurements of soils, the research provides conclusive evidence that the earthworks were built rapidly. Essentially, there is no evidence of boundaries or signs of weathering between the various levels, which would have occurred if there was even a brief pause in construction. This required a large labor force, organized and good leadership. These were hunter-gatherers coming together on a huge common goal. They mixed clay, silt and sand to avoid erosion due to being in a flood plain.
Phys.org has the report here;