Islamic civilization was once the envy of the world. From a succession of glittering, cosmopolitan capitals, Islamic empires lorded it over the Middle East, North Africa, Central Asia and swathes of the Indian subcontinent, while Europe cowered feebly at the margins. For centuries the caliphate was both ascendant on the battlefield and triumphant in the battle of ideas, its cities unrivalled powerhouses of artistic grandeur, commercial power, spiritual sanctity and forward-looking thinking, in which nothing was off limits.