The Nazca Lines
"Mysterious geoglyphs that span a vast swath of the rugged Peruvian desert, remain an engima. No one has proof as to who built them and what their function was. Since their discovery, the they have inspired fantastic explanations from ancient gods, a landing strip for returning aliens, a celestial calendar created by the ancient Nazca civilization -- putting the creation of the lines between 200 BC and 600 AD, used for rituals probably related to astronomy, to confirm the ayllus or clans who made up the population and to determine through ritual their economic functions held up by reciprocity and redistribution, or a map of underground water supplies.
There are also huge geoglyphs in Egypt, Malta, United States (Mississippi and California), Chile, Bolivia and in other countries." Quoted from: Crystalinks
Things of this nature bring into question the "mainstream" version of history we have been led to believe. I suggest watching these videos to get a better idea of how these incredible ancient geoglyphs may have come to be and what their true purpose was.
"No where is the evidence so strong that a technologically advanced culture existed on Earth in our ancient past, and in many cases evidence here may point to possible extraterrestrial influences that have shaped human history. This is the amazing story of the ancient Nazca Lines of Peru. Best seen from the air, the pictograms and linier formations stretch for miles across and defy explanation as to who made them and the method from which they were made."
The Mystery of the Nazca Lines: