More ancient than the pyramids: the giant mounds no one knows why they were built

About 5,500 years ago, hunter-gatherers in the southern United States built a vast complex of 11 earthen mounds, nearly a thousand years before the Great Pyramid of Giza. The site, Watson Brake in Louisiana, was built in stages over 600-700 years. Researchers know who built it, when and how, but its purpose remains a mystery.

About 5,500 years ago, nearly a thousand years before the Great Pyramid of Giza, a group of hunter-gatherers in what is now Louisiana began an enormous construction project. Without pack animals, metal tools or an organized agricultural society, they raised 11 earthen mounds and connected them with causeways that formed an elliptical complex about 300 meters in diameter. The site, known as Watson Brake and located near the city of Monroe, began to be built around 3500 BCE. Construction continued in stages for 600 to 700 years, and the tallest mound rises about 7.6 meters above its surroundings. The site was mapped only in the 1980s, and after dating tests were carried out in the 1990s it became clear how unusual it was: it is one of the oldest known earthen mound complexes in North America. The discovery changed the way archaeologists thought about the capabilities of hunter-gatherer societies, since for years it was accepted that large monuments require a settled agricultural society. The builders apparently used baskets, deer antlers and their hands to move enormous quantities of earth. The work required cooperation by large groups over generations. Archaeologist Vincas Steponaitis said that "the cases in which archaeologists find something that completely changes our picture of what happened in the past are rare" and that this site is exactly such a case. There is still no answer to the central question — why the complex was built. Food remains indicate a diet of fish, shellfish, deer meat, nuts and wild plants, with no agriculture. Stone tools, beads and objects made of fired clay were found, but no find explains the immense effort. Hypotheses include connecting communities, demonstrating capability, or responding to drought and flooding. Watson Brake itself is not open to the public.