A pair of grass covered mounds located on a Louisiana college campus have been deemed the oldest-known structures in North America after carbon data revealed construction on Mound B started 11,000 years ago and Mound A around 7,500 years ago – making them about 6,000 years older than the ancient Egyptian pyramids.
Constructed by indigenous people on what is now Louisiana State University (LSU) in Baton Rouge, the mounds stand about 20 feet tall and are believed to have been used for ceremonial purposes because they align with one of the brightest stars in the night sky – a red giant known as Arcturus.
The theory stems from discoveries of ash from burned reed and cane plants, as well as the burned bone fragments, found beneath the grass and dirt.
These mounds are among 800 man-made, hill-like mounds in the state that were built by indigenous people, however, many of the others have been destroyed.
Mound B, the oldest of the pair, is believed to have been built over a few thousands of years – layer by layer.
The mound was eventually abandoned around 8,200 years ago, which was determined by aging roots found in the sediment layer.