What gave Christopher Columbus the confidence in 1492 to set out across the Atlantic Ocean? What persuaded the king and queen of Spain to commission the voyage? It would be convenient to believe that Columbus and his men were uniquely courageous. A more reasonable explanation, however, is that Columbus was heir to a body of knowledge about seas and ships acquired at great cost over many centuries. 'Fish on Friday' tells a new story of the discovery of America. In Brian Fagan's view, that discovery is the product of the long sweep of history - the spread of Christianity and the radical cultural changes it brought to Europe, the interaction of economic necessity with a changing climate, and generations of unknown fishermen who explored the North Atlantic in the centuries before Columbus.