The Incas were a geat South American civilisation. Until the sixteenth century, they ruled nearly 1 million square kilometres of western South America. Then they disappeared. Not much is known about them because they didn't keep written record. But Reinhard has spent his life studying them. Before he found the three children on Llullaiaco, he found fifteen other Inca mummies on other mountains. He believes the frozen mummies were human sacrifices to the Inca gods.