For thousands of years, pyramids were the largest structures on Earth. The best known were constructed in Egypt and Central America, but others have been found all around the world, including in China, Africa and Indonesia. But what purpose did the pyramids serve? Researchers explore strange similarities between all pyramids, as well as the geographic, strategic and otherworldly connections between these mysterious monumental structures.

A young man's spiritual journey. A controversial bestseller. And a scientific theory that threatened to change the world. Just what are the facts behind Erich von Däniken and Ancient Astronaut theory? For more than 40 years, his books have sold over 65 million copies worldwide. He is a hero to some, and a heretic to others--but Erich von Däniken's controversial theories have captured the attention of the world and ignited a movement known as Ancient Astronaut Theory. His exhaustive search for the truth about mankind's otherworldly origins have started to gain acceptance with a small but growing number of Ancient Astronaut theorists--men and women who have expanded, and at times refined, von Däniken's findings. Did ancient astronauts really come to planet Earth? And, if so, what was their purpose? And perhaps even more important--will they come again?

Egyptian hieroglyphs depict the use of light bulbs in tombs and secret chambers. And batteries may have been discovered among artifacts from Mesopotamia. Did the Ancients understand electricity, and if so, how did they discover this technology? Might they have had help from extraterrestrials?

They were teachers and destroyers. Mighty warriors who blazed across the skies in gleaming chariots and wielded magical weapons that could bring down mountains. Odin, Frey and Thor. The gods worshipped by the Norse Vikings were fearsome and mysterious, but were these beings truly divine, or is there, perhaps, an extraterrestrial connection? The Norse were among the most technologically advanced cultures of the ancient world. They were epic explorers who embarked on oceanic voyages to Africa and the Middle East and even reached North America at least 500 years before Christopher Columbus. Were the Norse guided by powerful gods, or could the super-beings that guided the Vikings have actually been visitors from another planet?

Across the globe, archaeologists have uncovered ancient tombs filled with strange items and writings. Remarkable similarities have been found at each of the sites. How is it possible that the burial chambers of distant cultures were so similar in design? Ancient Astronaut theorists believe that some of these complicated and technically advanced tombs were designed with the help of extraterrestrials.

Massive stone structures that reach to the heavens... strange, giant figures buried deep in the Earth... and energy emitting spheres connected around the globe... What compelled ancient man to move colossal stones, in some cases weighing thousands of pounds, and to build remarkably similar stone monuments all around the world? From the jungles of Costa Rica to England's rural countryside, ancient people achieved extraordinary feats of construction without advanced tools or technology. Is it possible that extraterrestrials instructed the ancients to build these complex structures? Or were our ancestors driven to create these monoliths in order to reconnect with celestial travelers who once walked the Earth? Could ancient monoliths hold advanced, extraterrestrial powers we have yet to realize? And if so, just what will happen when we unlock the mystery of the monoliths?

In 1980, three young military men were sent into a UK forest to investigate strange lights. They reportedly encountered a spacecraft of unknown origin. When one of the men touched it, he claims to have received telepathically a long sequence of binary code, which he later wrote down and translated. The military ordered them to never speak about the incident. Why do such UFO encounters continue to be kept under wraps, and what might they reveal about our ancient past?

Why were ancient civilizations around the world so focused on the Orion constellation? While scientists site many earthly connections, researchers suggest this point in the night sky may have been a so-called Stargate, or entry point, for alien life forms. If extraterrestrials have been visiting Earth for thousands of years, might they have originated from the Orion Nebula?

Erich von Daniken's landmark book, Chariots of the Gods, brought attention to the mysterious phenomena of the Nazca Lines. Hundreds of gigantic lines, some in the shape of animals, geometric patterns and even an alien-like being, extend for miles throughout a remote Peruvian desert. Scholars are divided as to who built them, and why. Some Ancient Astronaut theorists believe that the massive markings have an extraterrestrial connection, and perhaps the ancient people of the region created these gigantic figures in tribute to the gods who visited them. And with one of the largest deposits of nitrates in the world--a key ingredient in rocket fuel and weaponry--could Nazca have been a mining operation for advanced beings in the distant past?

In 1975, Travis Walton claims to have been abducted and taken aboard a space ship inhabited by extraterrestrial beings. Several people witnessed his encounter and nearly 40 years later Walton's story of alien abduction, missing time and mind-telepathy manipulation has not wavered. But researchers say that abductions are not a modern phenomenon. The Hebrew Bible is filled with stories of abductions by otherworldly beings. Jonah, Moses, Ezekiel and Enoch all depict what can best be described as physically being taken to other dimensions and then returned. Is it possible that extraterrestrial beings have been abducting humans for thousands of years and if so, might there be an alien agenda behind the phenomena?

Was Albert Einstein a genius? Or was he superhuman? Was his genius ‘of this world,’ or was it ‘otherworldly?’ Is it possible, as Ancient Astronaut theorists believe, of an extraterrestrial connection to the scientific genius of famous historical figures such as Albert Einstein, Galileo, Archimedes, and Aristotle?

They were the messengers of divine knowledge and seers who shared visions of the future. For thousands of years, human civilization has been guided by the words and deeds of ancient prophets, but just who--or what--were these prophets communicating with? Might the experiences of history's prophets be evidence of communication with a heavenly source--or were seers like Elijah and Joseph Smith actually communicating with extraterrestrial overlords? And if so, are there similar prophets at work today?