The Alhambra, the 'red fort' on its rocky hill above Granada, with its fountained courts and gardens, and intricate decoration, has long been a byword for exotic and melancholy beauty. In a stimulating new book in the 'Wonders of the World' series Robert Irwin, Arabist and novelist, examines its engrossing and often mysterious history. Built by a bloody and threatened dynasty of Muslim Spain, it was preserved as a monument to the triumph of Christianity. Much of what we see is the invention of later generations. Its highly sophisticated decoration is not just random but full of hidden meaning. Even its purpose - palace or theological college - is not always clear. Its influence on art, and on literature, orientalist painting and Granada cinemas, Washington Irving and Borges, has been.