Why are the Nazca drawings one of the great mysteries of archaeology?

In the hot deserts of southwest Peru are some immense, mysterious drawings called geoglyphs. Huge geometric patterns, spirals and figures of animals, and thousands of straight lines are immaculately drawn on the desert surface. Known as the Nazca Lines, after the Nazca Indians who lived there in ancient times, the drawings have mystified scientists ever since they were discovered in the 1920s. From the ground level, the drawings seem like a confused mass of lines. Only when viewed from the air, they convey a definite pattern. Scientists feel they could represent an astronomical calendar, or were part of a religious ritual.