Peru's Mass Grave: The Ghosts of Kuélap

High in the cloud forests of Peru is the mountaintop fortress of a lost civilization ' and with it, an ancient legend of mass murder. The Chachapoya, or 'Cloud Warriors,' who lived here from A.D. 800 to the mid-1500s, nearly vanished without a trace, virtually overnight. For more than 400 years, anthropologists have been hunting for who or what killed these Osobnosti. Now, a discovery of a site with more than 80 corpses could solve this mystery. Explorer joins a team of scientists who believe the answer is hidden in the bones. We'll analyze the evidence and test the theories ' from an Incan massacre to an epidemic disease, ritual sacrifice or political assassination by a rival tribe ' and finally close the case on this lost capital's ultimate collapse. (National Geographic)