People still wonder WHY they built them, and scientists don't have all the answers... they aren't calenders or astronomical images (although SOME of them might be). It is very likely they were all about religion.
Then These guys built a hot air balloon, made entirely from stuff the Nazca could have gotten their hands on. Proving it was possible. Also, here is this quote from time magazine
The researchers also found a significant clue in documents at the University of Coimbra in Portugal. These papers revealed that in 1709 a Brazilian-born Jesuit missionary named Bartholomeu de Gusmao went to Lisbon and demonstrated (74 years before France's Montgolfier brothers flew their balloon over Paris) a model of a balloon believed to have been used by the Indians. Filled with smoke and buoyed by hot air from glowing coals in a clay pot, the replica rose from Gusmao's hand and floated toward the palace ceiling.Wow. Hot air balloons (possibly), in use for religious ceremonies (possibly), over a thousand years ago. I can just picture the Nazca version of a high priest and a member or two of the congregation going up in the air and seeing these shapes revealed below them... what an intense experience that would (possibly) be.
Read more: http://www.time.com/time/magazine/article/0,9171,879533,00.html#ixzz1IIX4D1Is
And people wonder why I stopped reading fiction.