Muhammad's successor the Caliph Umar decreed that Jews and Christians should be removed from all but the southern and eastern fringes of Arabia—a decree based on the uttering of the Prophet: "Let there not be two religions in Arabia". The two populations in question were the Jews of the Khaybar oasis in the north and the Christians of Najran. Only the Red Sea port of Jeddah was permitted as a "religious quarantine area" and continued to have a small complement of Jewish merchants. During the Caliphates During the Middle Ages, Jewish people under Muslim rule experienced tolerance and integration. Some historians refer to this time period as the "Golden Age" for the Jews, as more opportunities became available to them. In the context of day-to-day life, Abdel Fattah Ashour, a professor of medieval history at Cairo University, states that Jewish people found solace under Islamic rule during the Middle Ages. The Muslim rule at times didn't fully enforce the Pact of Umar and the traditional Dhimmi status of Jews; i.e., the Jews sometimes, as in eleventh-century Granada, were not second-class citizens. Author Merlin Swartz referred to this time period as a new era for the Jews, stating that the attitude of tolerance led to Jewish integration into Arab-Islamic society. Social integration allowed Jews to make great advances in new fields, including mathematics, astronomy, philosophy, chemistry and philology, with some even gaining political power under Islamic rule. For example, the vizier of Baghdad entrusted his capital to Jewish bankers, Jews were put in charge of certain parts of maritime and slave trade, and Siraf, the principal port of the caliphate in the 10th century, had a Jewish governor. Increased commercial freedom increased their integration into the Arab marketplace. Leon Poliakov writes that in the early ages of Islam, Jews enjoyed great privileges, and their communities prospered. No laws or social barriers restricted their commercial activities, and exclusive trade and craft guilds like those in Europe did not exist. Jews who moved to Muslim lands found themselves free to engage in any profession, resulting in less stigma than in Europe where such restrictions were still in force. This, coupled with more intense Christian persecution, encouraged many Jews to migrate to areas newly conquered by Muslims and establish communities there. Although Jewish life improved under Islamic rule, an interfaith utopia did not exist. Jews still experienced persecution. Under Islamic Rule, the Pact of