This is Not the End of the Book:

The extraordinary historical consequences of errors and fictional inventions. SERENDIPITIES is an iconoclastic, dazzlingly erudite and witty demonstration, by one of the world's most brilliant thinkers, of how myths and lunacies can produce historical developments of no small significance. In Eco's words, 'even errors can produce interesting side effects'. Eco's book shows how: -- believers in a flat earth helped Columbus accidentally discover America -- the medieval myth of Prester John, the Christian king in Asia, assisted the European drive eastward -- the myth of the Rosicrucians affected the Masons, leading in turn to the widespread belief in a Jewish masonic plot to dominate the world and other forms of paranoid anti-Semitism in the nineteenth and twentieth centuries.