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