This week Ancient Aliens looks in to the possibility that extraterrestrials might either constructed or at least aided in the building of many ancient structures.
Ancient Astronaut theorists believe that some time in the distant past our ancestors were contacted by aliens, who then helped them build many of the ancient wonders of the world.
They point to the undeniable similarity in the design of structures on opposite parts of the planet, at a time when there was no known contact between the civilisations concerned. Whether this is the pyramid of Giza in Egypt, Baksei Chamkrong in Cambodia or the Avenue of the Dead in Teotihuacan, Mexico.
Could aliens, perhaps even disguised as gods, have somehow given ancient builders a blueprint for these structures or is the pyramid? For instance Baksei Chamkrong is dedicated to the Hindu god Shiva and many theorist believe Shiva was actually an alien leader.
Sceptics point out that the pyramid is a natural shape to use if you are looking to build a very large structure, since its shape gives stability by spreading out the weight. You only have to pile up some sand to see this working in practice, if you build the sides at too a steep an angle the structure will collapse without additional support, so the pyramid is ideal.
However, others remain convinced that it is just too much of a co-incidnece for these similarly shaped structures to have appeared all over the world.
Ancient Aliens airs Fridays at 9:00 PM on History Channel.