Throughout the ancient world, tales were told of fire-breathing dragons. Though fearsome, they were often worshipped as the bringers of great knowledge and credited as the founders of civilization. Is it possible that what our ancestors described as winged monsters descending from the sky were visitors from other worlds?

Ancient Aliens has traveled to many mysterious sites that seem to defy explanation. Now, Giorgio Tsoukalos takes a look back at some of the most incredible structures we've visited all over the world. Structures that, as far as Giorgio is concerned, provide undeniable evidence of extraterrestrial contact.