Until their conquest by the Spanish in the 16th century, the Incas built up a 2,000-mile empire, with cities perched on mountaintops, irrigated terraces clinging to the sides, and a network of roads carved through some of the most difficult terrain in the world - all in less than a century. Today archaeologists are digging behind the myths and legends that surround the Incas to discover how their enormous empire was actually run. Dr John Hyslop is studying the road system, probably the most extensive ancient road system in the world. Dr Craig Morris is studying the administrative centres and Dr Ann Kendall is excavating near the most spectacular of all Inca sites - Machu Pichu. But can their research do more than tell us about the Incas, can they also help to re-populate areas of Peru which once flourished, but where now only a few families live in extreme poverty? Re-aired 31 March 1982