Erich von Daniken undertakes to prove that in prehistoric and early historic times the Earth was visited by unknown beings from the Cosmos; that these extra-terrestrials created human intelligence by a deliberate genetic mutation; that the extra-terrestrials ennobled hominids 'in their own image'; that these visitors to Earth were recorded and handed down in various religions, mythologies and popular legends; and that in some places, the extra-terrestrials left physical evidence of their presence on Earth. He draws his evidence from all over the world: from the Turkish mountains where carved monoliths and giant stone heads mysteriously survive the centuries; to the secret caves of Ecuador, where treasured remnants of a bygone era remain hidden; to equatorial Africa, where the 'primitive' Dogon have been familiar for centuries with the complex movements of Sirius, a star only discovered by western astronomers since the invention of the radio telescope. He searches the ancient documents of the Hindus, the Jews and the Christians; examines religions, mythologies and legends and fins a recurring theme of 'human' gods, heavenly chariots, 'space suits', floods and disasters. The evidence is largely circumstantial - but he challenges all comers to produce an interpretation that better fits the facts. Illustrated with black and white photographs.