Because they weren't there before...

My admiration for the early American civilizations increased markedly after reading "1491" and hence I was struck by this weird story.

While the world is generally familiar with Machu Pichu and the Nazca Lines, another mystery has come to light through the modern science of satellite photography. This phenomenon is one that was previously known but the extent of its size and effort required to make it is just being fully realized.

A series oh holes, usually about 24 inches across and in neat rows of from nine to twelve, stretched for almost a mile in Peru. It starts at the base of a mountain and then climbs up the side and meanders up and down, over some of the roughest terrain. [More]

We have a tendency to grossly underestimate both the capabilities and intelligence of ancient people. Still, discoveries such as this suggest we ourselves may one day be sadly misunderstood as well.