Ancient Aliens: Season 18, Episode 2

18 - 2: Mystery of the Standing Stones

It is one of the greatest mysteries of the prehistoric world: why did people on nearly every continent erect giant standing stones? According to Ancient Astronaut Theorists, the placement of these monoliths and their geological makeup could point to extraterrestrial intervention--and. quite possibly, a technology that once existed on Earth far more advanced than our own.