Born Rai, Persia, 786; died Tus, 809. The 5th and most-renowned of the Abbassides. Under him the Eastern Caliphate attained the height of its splendor with Baghdad as the center of learning and culture, and extended from the Jaxartes and Indus to Gibraltar. He invaded Greece, forced Nicephorus to pay tribute to him, and acknowledged the protectorate of the Franks over the Christians in Jerusalem by delivering to Charlemagne the keys of the Holy Sepulchre, the banner of Jerusalem, and some precious relics. He is best known as a hero of "Arabian Nights."