Ancient astronaut theory

The ancient astronaut theory says that human beings are either the descendants of aliens who landed on Earth millennia ago, or that much of our culture was given to us by extraterrestrial visitors in the time of pre-history. Evidence often consists of allegatations that ancient monuments, such as the pyramids of Egypt or Machu Picchu in Peru, could not have been built without technical abilities beyond those of people at that time.

Although not taken seriously by mainstream science, this theory has many adherents, and many variations. It has been popularized by best-selling authors such as Erich von Daniken and Zecharia Stichin.