Site · North America · United States
Serpent Mound
Radiocarbon in 1991 made Serpent Mound about 900 years old. A 2014 team said 300 B.C.
In 2014, radiocarbon dating determined the mound was built in 300 BCE by the Adena…
Did the builders know?
Photo: Stephanie A. Terry, CC BY-SA 4.0, Wikimedia Commons