The Nazca lines are giant drawings in the earth, or geoglyphs, located in the Nazca desert in Peru. They were built by members of an ancient culture that inhabited the area between the 4th and 8th centuries BCE. The Nazca lines consist of hundreds of figures, each drawn with a single line, many in the shape of animals. The most mysterious feature of the Nazca lines is that the pictures they form are only visible from high up in the air; some of the figures measure 900 feet (270 meters) across.

The Nazca lines are classified as negative geoglyphs. That is, they were made by removing part of the ground's surface, rather than by adding dirt or gravel. The surface of the Nazca desert is covered with rusted pebbles, which the ancient Nazca people removed to reveal lighter soil underneath. The dryness and lack of wind in the Nazca desert have kept the Nazca lines extremely well preserved over the centuries.

Why the ancient Nazca people would create elaborate geoglyphs so large that no one could see them has puzzled researchers since the discovery of the Nazca lines. The leading theory is that the Nazca lines were religious in nature, meant to be visible to gods residing high in the sky. Proponents of this theory often suggest that the Nazca lines served not only as messages to the gods, but also as paths leading to and from places of worship.

Other theories regarding the ancient purpose of the Nazca lines are varied. One of the most controversial, popularized by author Erich Anton Paul von Däniken, is that extraterrestrials helped the Nazca people build the geoglyphs as landing strips for their aircraft. Others have suggested that the ancient Nazca people developed rudimentary methods of flight, most likely a hot air balloon.

One of the earliest theories proposed that the Nazca lines were a form of astronomical chart, but there is insufficient evidence to support this idea. A similar theory points to a period of frequent solar eclipses in the Nazca desert around the time the lines were built; the Nazca people may have interpreted the phenomenon as a giant eye observing them from the sky and built the Nazca lines for its benefit. Another theory that has gained some popularity is that the Nazca lines served as a map of underground waterways, which would have been quite valuable in the desert.