The Aztecs built one of the world's most powerful and feared empires and they claimed that they were guided by a pantheon of more than a thousand gods who came to Earth from different parts of the universe. Could the incredible story of their rise to power and their sudden demise, reveal a history of extraterrestrial intervention in Mesoamerica?

Puma Punku in Bolivia features stone blocks, each carved with precision; the blocks lie scattered across the landscape, confusing archaeologists as to what the ancient site might have been.

Considered by many to be the greatest civilization in the history of the Americas, the Maya thrived for more than 2,000 years. Now, new evidence is being discovered that completely upends our understanding of this ancient culture... and might provide evidence that the Maya came in contact with extraterrestrial visitors.

For more than four decades, award-winning journalist Linda Moulton Howe has covered the most mysterious phenomena on Earth. Could her investigations on everything from bizarre animal deaths to crop formations and alien abductions lead us to a profound new reality?

Deep beneath the sands of Egypt lie 24 enormous sarcophagi, and every one of them is empty; discussing what purpose those giant tombs had served.

For thousands of years, humankind has attempted to make contact with beings from beyond Earth; now, the search for extraterrestrial intelligence is ramping up, with new technologies allowing individuals to explore the universe.

Dr. Jacques Vallée has many scientific degrees, is a best-selling author and is regarded as one of the internet's founding fathers. But he is best renowned for his groundbreaking work on the subject of UFOs, where his bold theories call into question our understanding of alien life.

Ancient Aliens is counting down ten of the most astonishing and unexplainable technologies in history. From mysterious golden orbs discovered in Mexico, to a sacred wooden box that could communicate with the heavens and an ancient tomb that is said to depict an astronaut. Might these sensational artifacts be evidence of otherworldly contact?

Across the globe, reports of mysterious glowing orbs are on the rise. Their movements frequently defy the laws of physics and now they are even being reported near military bases, ships and nuclear weapon facilities. Do they represent a non-human intelligence and if so, why are they here?

In the early 1900s, a modern-day prophet from the hills of Kentucky became a worldwide sensation: Edgar Cayce. He claimed to receive visions of both the past and the future while in a trance, he healed the sick, and alleged to have encounters with otherworldly beings. Could it be that Edgar Cayce was a vessel used to carry out an alien agenda?

For thousands of years, cultures around the world have held a belief in stargates through which beings have traveled to Earth from distant points in the universe and even other dimensions. Could such portals truly exist? And if we obtain the key to unlocking the stargates, will we find a cosmos teaming with life?

The discovery of the ancient megalithic site of Karahan Tepe in southern Turkey turned the world of archaeology on its head, displaying engineering skills far beyond what the people of the time were thought to be capable of. But could new evidence reveal that this more than 11,000-year-old complex was built not by humans…but giants?

For decades, incredible claims have been made about an extraterrestrial presence on Earth, and the government has gone to great lengths to discredit them.

Stories of god-like beings providing instruction to early humans, helping establish the first civilizations; exploring if mysterious figures who appear throughout history provide evidence that these otherworldly teachers have been here all along.

Many of the architectural marvels of the ancient world bear striking similarities to one another, even though they were built by civilizations that were separated by thousands of miles and are believed to have had no contact with one another. Separated by more than 7500 miles, the Giza pyramid complex in Giza, Egypt and the Avenue of the Dead in Teotihuacan, Mexico contain pyramids that are aligned with the constellation of Orion's belt. An ancient pyramid temple in Cambodia known as Baksei Chamkrong is an almost identical match for the Temple of the Jaguar in Guatemala. Many structures built using stone slabs that weighed over a hundred tons. But how did primitive people achieve such extraordinary feats? And why do we see such similarities? Could these sites have all been designed by alien architects?

In the 20th century, a mysterious British woman who claimed to be the reincarnation of an ancient Egyptian priestess shocked Egyptologists by accurately locating countless structures and artifacts in the Nile Valley. Could it be that she was carrying out an otherworldly agenda–and preparing for the return of the Egyptian gods?

Terrifying encounters at 40,000 feet. Pilot accounts of UFOs taking control of their aircraft. Entire jumbo jets disappearing into thin air. Since the dawn of aviation, pilots have experienced unexplainable events in the sky. Could they have witnessed aliens in our airspace?

In the 21st century, UFOs have gone from fringe science to mainstream obsession. A new generation of UFO hunters is employing incredible technology, and Unidentified Flying Objects are being openly investigated by the government. Are we closer than ever to understanding the strange events happening in our skies?

More than 7,000 years ago, the ancient Sumerians established what is considered the world's first civilization and they credited their extraordinary achievements to their gods, the Anunnaki. But is it possible that these powerful beings were, in fact, extraterrestrial visitors to Earth?

From biblical patriarchs to modern day alien abductees, throughout history, there have been people who claimed to have contact with otherworldly beings; often bearing important messages for humanity.

At nearly 14,000 years old, the ruins of Puma Punku are the oldest and most baffling on the face of the Earth. No one knows who designed and built this complex of sophisticated inter-locking blocks, and then vanished. Researchers investigate the ruins on-location in Peru and present new computer analyses. Forensic evidence on the ground, together with local myths and legends, suggest this site may have been designed and even once inhabited by a species of extraterrestrials.

Is there evidence of ancient technology buried beneath the ice of the most southern continent?

Within 20 years, we are expecting to send the first colonizers to the Red Planet. Astronauts will brave the six-month journey to become the first extraterrestrials visitors to Mars--where they are expected to live and die there, never to return to Earth. But why have we always had a strange fascination with this particular planet? The latest NASA research has revealed that not only is there evidence of liquid water on the planet, but that life on Earth was most likely seeded on Mars. Ancient Astronaut theorists even suggest that the development of life on Earth may have similarities to how scientists are currently planning to keep humans alive on the red planet. Could extraterrestrials from Mars have colonized Earth in our remote past? Could our voyage to Mars not only unlock the mysteries of our ancient, extraterrestrial origins--but also be the key to the long-term survival of the human species?

It was mankind's finest hour, the greatest technological achievement of the 20th Century--the Apollo 11 mission to the Moon. But the Apollo program was short-lived, and after Apollo 17 in 1972, we never went back. Could it be that we encountered something--or someone--on the Moon? Did the Apollo astronauts witness more than NASA wants us to know? The Moon is the most visible celestial body in the night sky and is essential to life on Earth. But what if the Moon is not the natural object we believe it to be? Unidentified lunar objects in NASA photography may point to extraterrestrial structures on the moon, and possibly evidence of what lies beneath the surface. Some Ancient Astronaut theorists have even suggested that the Moon is actually an artificial object, placed in its current position by otherworldly beings thousands of years ago.

Giorgio Tsoukalos and David Childress explore the mysterious chain of manmade islets in Micronesia's Nan Madol; built from 250 million tons of volcanic rock, there are local legends that strange visitors floated the massive rocks through the air.