Dyarchy. The word sultan appears in the Qur'an, but only in the meaning "authority" or "proof," never as the title of a person. During the early centuries of Muslim rule, the ruler— because he possessed "authority" and sovereignty—was occasionally called the sultan, but the conversion of the word into a title of office for a supreme ruler dates to its use by the Saljuk Turkish sultans, who in the period 1055-1152 dominated the Muslim East, including Baghdad, which was then still the Muslim metropolis. By using the title sultan the Saljuks recognized the theoretically superior authority of the khalifah but exercised all the real power for themselves. Therefore, the Saljuk period introduced to Muslim politics the concept of dyarchy (a government with two rulers): the khalifah was the higher, spiritual head of the Muslims with control over creed, while...