Mexico's Temple of Quetzalcoatl, or the Feathered Serpent ... suggesting that many ancient mysteries are evidence of early human contact with extraterrestrials. Some fringe theories, including ...

Built between the 1st and 7th centuries A.D., it is characterized by the vast size of its monuments - in particular, the Temple of Quetzalcoatl and the Pyramids of the Sun and the Moon, laid out on ...