Are they evidence of an advanced early civilization that history never recorded? Are they proof that early man had contact with extraterrestrials? Is it a giant scientific or mathematic equation? Did UFOs once land in a remote corner of South America? To this day, the famous Nazca Lines in southern Peru pose more questions than answers. They are one of history’s most intriguing puzzles.

Sixty years ago, Nazca was a dusty small town in the middle of the desert south of Lima. The locals had long known of some of the ancient piles of stones outside of town on the pampa, or flat desert plain, but they didn’t know they were in the middle of what would become one of the world’s great mysteries.

That all changed in 1939 when Paul Kosok, a water irrigation scientist from the United States, was flying over the region in a small plane. From his vantage point in the sky, he was the first person to look down and see the unusual lines on the pampa.

At first, Kosok believed that the lines outlined an ancient irrigation system. But then he made another pass of the area and noticed that one line pointed directly to the setting sun. By an unusual twist of fate, the day Kosok flew over Nazca was the summer solstice. He later called Nazca “the biggest astronomy book in the world.”

Another fateful chance came later in Lima, when Kosok was giving a speech about his findings. A young German woman, Maria Reiche, was serving as his Spanish translator. After talking with Kosok, she became obsessed with the Nazca Lines and wound up devoting her entire life to their research. Reiche spent her adult years walking and measuring in the desert, tracing the lines and making detailed calculations of each design. She lived simply in a hotel in town and gave talks about the lines each evening. She died in June 1998 but is still revered in Nazca and, really, all of Peru.

Reiche and other researchers concluded the lines were made by the Nazca Pre-Incan culture between 300 B.C. and 700 A.D. Since the Nazca pampa has an almost complete lack of windy weather or rain, the stone piles that make the lines have withstood the elements for thousands of years.

The Nazca Lines have now been photographed and videotaped thousands of times. While there are hundreds of perfectly straight lines, not all of the Nazca Lines are lines at all. The most intriguing designs are of animals, some up to 1,000 feet wide. The most famous is probably the monkey, with its curled tail. Other designs include a spider, condor, hummingbird, whale and dog.

So why were the lines built?

There have been many different theories and scores of books and papers written about the Nazca pampa. But, to this day, no one can say with certainty why they were built. It only fuels the mystery and leaves visitors intrigued.

The leading explanations: