A Tunisian aristocrat named Abd al-Rahman Ibn Khaldun, after a stormy career in politics, retired to a castle in Algeria in 1375 and began to write a history of the world. Before embarking on his narrative, however, he gave unhurried thought to the nature of human history. That thought, set down in lengthy Muqaddimah (introduction) to his history, has won him a peerage among mankind's great thinkers. Arnold J. Toynbee has pronounced it “the greatest work of its kind that has ever yet been created by any mind in any time or place.”