Potential alien influence on the Mayan culture, including its disappearance and legacy.

The end of the Mayan Long Count Calendar and potential alien explanations for what may come.

Beings with big heads and giant eyes are called the greys and have been depicted in ancient art.

Natural disasters in the ancient world may have originated with the meddling of celestial beings.

Research into alien contact in the recent past including evidence from astronauts and scientists.

44min | Aired on Mar 09, 2012 | TV-PG | CC

A 14,000-year-old set of ruins with complex interlocking blocks defies earthly explanation.

Some theorize that Bigfoot is connected to an alien species that visited in ancient times.

Examining Leonardo da Vinci's paintings, sketches and journals looks for alien technology.

The possibility that alien sightings may be evidence of time travelers from the future.

Angkor Wat, Cambodia, world's largest ancient temple, curiously has a picture of a stegosaurus.