general chronological framework for the process of conversion of Iranians to Islam. From a study of the probable dates of individual conversions based on genealogies in biographical dictionaries, Richard Bulliet has suggested that there was gradual and limited conversion of Persians down to the end of the Umayyad period (132/750), followed by a rapid increase in the number of conversions after the ʿAbbasid revolution, so that by the time when regional dynasties had been established in the east (ca. 338/950) 80 percent or more of Iranians had become Muslims. The data on which Bulliet's study was based limited the validity of this paradigm to generalizations about full, formal conversions in an urban environment. The situation in rural areas and individual regions may have been quite different, but the overall pattern is consistent with what can be deduced from traditional historical sources. Although in some areas, for example, Shiraz at the time of Moqaddasi's visit in about 375/985 (p. 429), there may still have been strong non-Muslim elements, it is reasonable to suppose that the Persian milieu as a whole became predominantly Islamic within the period of time suggested by Bulliet's research. Islamization of Iran Following the Abbasid revolution of 749–51, in which Iranian converts played a major role, the Caliphate's center of gravity moved to Mesopotamia and underwent significant Iranian influences. Accordingly, the Muslim population of Iran rose from approx. 40% in the mid 9th century to close to 100% by the end of 11th century. Islam was readily accepted by Zoroastrians who were employed in industrial and artisan positions because, according to Zoroastrian dogma, such occupations that involved defiling fire made them impure. Moreover, Muslim missionaries did not encounter difficulty in explaining Islamic tenets to Zoroastrians, as there were many similarities between the faiths. According to Thomas Walker Arnold, for the Persian, he would meet Ahura Mazda and Ahriman under the names of Allah and Iblis. Muslim leaders in their effort to win converts encouraged attendance at Muslim prayer, and allowed the Quran to be recited in Persian instead of Arabic so that it would be intelligible to all. The first complete translation of the Qur'an into Persian occurred during the reign of Samanids in the 9th century. Seyyed Hossein Nasr suggests that the rapid increase in conversion was aided by the Persian nationality of the rulers. According to Bernard Lewis: "Iran was indeed Islamized, but it was not