The desolate plains of the Nazca Desert guard a secret that has preoccupied researchers for decades. Over a thousand years ago the desert agriculturists of Nazca (100 BC to AD 750) traced miles and miles of shallow lines on the Pampa Colorada ("Red Plain") in the form of giant animals, geometric shapes and straight lines. The majority being visible only from the air, the geoglyphs remained unknown for many centuries until people in an airplane spotted them by chance in the 1930s. And yet why would the Nazca, a civilization who apparently had no means of viewing their own designs from the air, go to the effort of creating hundreds of such enormous figures?

First, let's consider the less formidable question of how the Nazca people managed to create these puzzling geoglyphs. The surface of the Nazca Desert consists of dark reddish-brown stones with light-colored soil underneath, so what they did to create a visible contrast was simply clear the stones away. As far as creating figures on a large scale, they likely made use of basic surveying equipment and tools like wooden stakes and grids. Just as their weavers made use of grids to create ornate woven designs, those responsible for the geoglyphs probably used a grid system to replicate small images on a larger scale.

The animals the Nazca chose to depict on the desert floor include monkeys, spiders, birds, sharks, whales, llamas and lizards. Plants and humans are also represented. The most numerous geoglyphs, however, consist of geometric shapes such as triangles, trapezoids, circles, spirals and straight lines that stretch up to nine miles long. A few of the images, including human forms, were etched into steep hillsides rather than on flat ground. One might wonder how it is possible that such superficial, impermanent drawings could survive in such excellent condition over so many hundreds of years, but the answer lies in the erosion-free desert climate. The Nazca Desert is one of the driest places on Earth, which combined with its lack of wind and constant year-round temperatures of 77°F, makes for optimal preservation of the geoglyphs.

But what could the purpose behind these huge images have been, and why are there so many of them? There's still no consensus among specialists, but most believe them to hold religious significance. According to Johan Reinhard, the Nazca people worshiped mountain gods, who were believed to control the weather (hence the water supply) and protect humans. The geoglyphs were supposedly associated with the worship of these deities, the geometric designs representing water flow and the biomorphs symbolizing fertility. The straight lines could have been sacred paths leading to shrines where these gods could be worshiped.

Others have offered less plausible theories. Paul Kosok proposed the designs were huge astronomical observatories, Henri Stierlin believed them to be giant looms and David Johnson and Steve Mabee hypothesized that the geometrical designs map out the underground sources of water. Still others have claimed the geoglyphs to be evidence of human or alien flight. Jim Woodman suggested that the lines indicate that the Nazca developed some sort of flight technology, such as hot air balloons, and Erich von Däniken went so far as to postulate that they were an ancient airfield used by extraterrestrials for landing their spacecraft. So far, no archaeological evidence has turned up in support of such unorthodox theories.