The reign of the caliph Harun al-Rashid is entwined with history and legend. This chapter disentangles the influences of the Arabian Nights and Orientalism on this caliph's biography, and explores his pursuit of a centralizing policy that culminated with the overthrow of the Barmakid ministers and the establishment of his base in Raqqa. The caliphate of al-Rashid evokes a wide range of themes dealing with international trade, Byzantine war, foreign embassies to Charlemagne, and a contentious plan for caliphal succession between his sons, al-Amin and al-Ma'mun.In spite of a civil war, the caliphate recovers under al-Ma'mun and goes on to experience an age of scientific englightenment sparked by the famous Greek to Arabic translation movement centered on classical texts. Al-Ma'mun's interest in philosophy, and his support for the rationalizing sect of the Mu'tazila, however, culminates with a backlash from traditionalist scholars and a standoff in the episode known as the Mihna.