Language. Middle Persian, or Avestan, was a written language during the entire twelve centuries of the ancient Persian empires (550 B.C.E. - 651 C.E.), and some of the ancient literature in that language is still read by followers of the Zoroastrian religion. But after the Muslims established control of most of Iran (638-651), the Avestan language lost the state patronage that was important for its survival. The decline of Avestan was accelerated by the Arabicization of public records that began during 700-742 in different areas of the khilafah. As Iranians began to adopt Islam, especially in northeastern Iran, Arabic became the primary language for all kinds of writing while Persian remained the spoken tongue of the people, including Muslims. Indeed, even the descendants of the original Arab immigrants to Iran and the rest of the Muslim East came to speak Persian as their...