Now one of the most popular tourist destinations in the world, Machu Picchu's original purpose is still unknown—though many archaeologists think they are closer to finding an answer. (Take a Machu Picchu quiz.)

Here are some of the top theories about Machu Picchu proposed—and in some cases disproven—in the century since its "rediscovery."

During his lifetime, Bingham, of Yale University, had two theories regarding the purpose of Machu Picchu. The first—that it was the birthplace of Inca society—came about when he was led to the site by local farmers in 1911.

(Read about the 1911 rediscovery of Machu Picchu.)

Bingham later modified that theory and suggested the site was also the legendary "lost city" of Vilcabamba la