Machu Picchu, in Cuzco, is one of the most famous archaeological sites in South America. The precise dating of the monumental complex, however, relies largely on documentary sources. Samples of bone and teeth from individuals buried in caves at four cemeteries around Machu Picchu form the basis for a new programme of AMS radiocarbon-dating. The results show that the site was occupied from c. AD 1420–1532, with activity beginning two decades earlier than suggested by the textual sources that associate the site with Emperor Pachacuti's rise to power in AD 1438. The new AMS dates—the first large set published for Machu Picchu—therefore have implications for the wider understanding of Inca chronology.