The sporadic attacks of the Muslim Arabs on the Sassanid territories ultimately resulted in two decisive battles in Qādesiyah and Nahāvand in which the Sassanid army was defeated while the downfall of the Sassanian Empire came subsequently in the year 21 AH/642 AD. However, the conquest of the Iranian territories was a gradual process that took several years during which the Muslim armies advanced eastwards. According to the historical records of historians like Tabari and Belāzari, as and when any city was conquered, the Muslims would negotiate with the local ruler and would ask him to choose from any of the following three options: a) to embrace Islam and gain safety; b) to remain on their own faith and pay the jizyah; or c) to fight and let the outcome of the war determine their fate. In case the people of a region chose to embrace Islam they only had to pay an income tax that would be levied on their incomes from the agricultural lands and, alternately, if they wished to remain on their own faith they would need to sign a peace treaty on the basis of which they would be considered as the dhimmi non-Muslims and would be required to pay the jizyah besides the regular taxes and would, in return, fall under the protection of the Islamic state and would be free to practice their own religious rites while the Muslims were not allowed to bother them in their celebrations and religious festivities. Needless to say, one more option would be to confront the Islamic army. Both Tabari abd Belāzari have recorded the texts of a number of such peace treaties and have made mention of the conflicts that took place in various parts of Iran. Although there have always been disagreements among the Muslim scholars (both Shiite and Sunni) as regards the Zoroastrians being “Ahl-e Ketāb” (lit.: “people of the book”), the followers of the Zoroastrian faith have always been treated like the other dhimmi (Ahl-e Ketāb) non-Muslims.
Generally, after conquering the Iranian cities and getting established in them the Muslim conquerors would continue with the Sassanid system of taxation and would even make use of the local tax officers and auditors. The language of the tax registers was initially Persian but when Hajjāj bin Yusof Saqafi come to power he changed it into Arabic.
During the early decades of the conquest of Iran at the hands of the Arab Muslims the pace of conversion to Islam was rather slow and in most regions, and particularly in the rural regions of western Iran, Zoroastrians constituted a majority while the Muslims (the new converts as well as the Arabs) lived in small communities among the Zoroastrian majority. However, this trend gradually changed and as a result of the interaction with the Muslims, the trend of embracing Islam gathered momentum, particularly in the urban areas. Moreover, with the conversion of large landowners and agriculturists – who probably converted to Islam in order to evade paying the jizyah – the agricultural laborers who worked on their lands, too, began to embrace Islam. Besides, the desire for gaining better social and economic conditions marked another factor that accelerated the pace of conversion to the new religion. Muslim historians like Estakhri and Moqaddasi have reported that during their times a majority of the people of an extensive part of Iran that was referred to as Fārs were still Zoroastrians and that there was no city or settlement that did not have fire temples. The Zoroastrian traditions were still practiced and people decorated the markets during their festivities. In addition, in some regions like Tabarestān the Zoroastrian local rulers who were popularly known as the “espahbodān” continued to stay in power until the 5th Century AH/11th Century AD.
During the period of the “Kholafā-ye Rāshedin” (the first four caliphs) and, consequently, during the reign of the Ummayids even though at times people were persecuted to change their religion or their fire temples were destroyed, the Zoroastrians, nevertheless, lived in relative welfare and freedom. The Islamic state had even granted recognition to the leader of the Zoroastrian community who lived in Pārs and was known as the “Hudinān Pashubāi” (lit.: “leader of the pious”) and had vested in him the responsibility of administering the affairs of the community. During the same period, a group of Zoroastrians migrated to the Qahestān region of Khorāsān and settled in Khavāf where they lived for almost a century. However, as time went by, it became difficult for the Zoroastrians to continue living there and, thus, they left Khorāsān for Bandar-e Hormoz and after staying there for a period of fifteen years, migrated to India by ship in the second half of the 2nd Century AH/8th Century AD in the wake of the attack of Rabi’ bin Ziyād’s army on Bandar Hormoz. This group of Zoroastrians first arrived in Sanjān in Gujarat (India) and, thereafter, settled in such cities as Navsāri, Surat, and Mumbai and, over the centuries, constituted the Zoroastrian (Pārsi) minority of India. A detailed account of this migration has been composed in the form of a poem called the “Qesseh-ye Sanjan” (lit.: “The Sanjān Episode) by a person known as Bahman Keyqobād. Despite living in that country for centuries, the Parsis of India continued to preserve their relations with the Zoroastrians living in their homeland and would even send them their written religious queries to which they would receive appropriate answers. This exchange of questions and answers was later on compiled in two books called the “Rivāyat-e Dārāb Hormazdyār” and the “Rivāyat-e Hormazdyār Farāmarz”.
During the early Abbasid period, and particularly during the reign of Ma’mun, the Zoroastrian community gathered fresh strength and by participating in religious and theological debates and dialogues – which for most part took place in the presence of Ma’mun – began to propagate the principles of the Mazdayanian faith. It was during this period i.e. between the 3rd and 4th Centuries AH/9th and 10th Centuries AD, that some important Zoroastrian books like the Dinkart, the Bundahishn, Select Parts of the Zādesparm, Manuchehr’s Works (letters of the “Dādestān-e Dini”), the Gojastak Abālish, and especially the Shekandgomānik Vezār (a report written by Gamān Shekan rejecting Islam, Christianity, Judaism, and Manichaeism) came to be written by the Zoroastrian scholars. Similarly, it was during this period that some prominent Zoroastrian thinkers like Ātur Faranbagh Farrokhzādan, Manushchehr Goshn Jam, Omid Āsheh Vahishtān, Āturpāt Eymidān (Emidān), and Mardān Farrokh Ohrmazd Dādān emerged. Moreover, a number of Zoroastrians – some of whom later on embraced Islam – as well some Muslims who came from Zoroastrian families were among the renowned scholarly figures of the Abbasid period. Some of the most prominent of such scholarly personalities were Nobakht and his son, Ibn Moqaffa’, and Ali bin Abbās (popularly known as “Majusi”).
In the early decades of the Abbasid rule, a particular intellectual reform was started in Khorāsān by a person called “Bahāfarid Māh Farvadin”, the effects of which prevailed for decades to follow. Bahā Farid’s aim was to make some changes in the Zoroastrian faith and, in this manner, bring about a compromise between Zoroastrianism and Islam. However, this innovative move enraged the Zoroastrian mobeds who complained to Abu Moslem, upon whose orders Bahā Farid was subsequently arrested and executed.
During the same period, some sporadic uprisings took place under the leadership of Iranians like Sonbād, Ostādsis, Bābak, and Māziyār in which the Zoroastrians played an active role. It is interesting to note that the nfluence of Bahā Farid’s intellectual reforms could be traced in all these movements. Towards the end of the Abbasid rule, some unjust and hard laws – such as the law enforcing the inheritance of a deceased Christian to be transferred to any of his sons who had converted to Islam – came to be imposed on the dhimmi non-Muslims, including the Zoroastrians, bringing on increasing poverty and economic hardships to this community.
Not much information is available on the social conditions of the Zoroastrians during the reigns of the Ghaznavids and the Seljuqs and it seems that since the Zoroastrian community had shrunk quite considerably and mainly because the Zoroastrians were not involved in the political affairs of the country, the historians did not pay any attention to the this community. During the Mongol invasion of Iran, and thereafter during the time of Teimur (Tamerlane) and his successors the Zoroastrians, too, met the same fate as the rest of the Iranians and were subjected to plunder and massacre. Apparently, it was under such circumstances that the rest of the Zoroastrians who still lived in Fārs migrated to the far off and remote mountainous regions of north Yazd along with the “Mobed-e Mobedān” (chief priest) and a group of their religious personalities and settled down in the villages of Sharif ābād and Torkābād, in order to save themselves from persecution. In this way, the Zoroastrian religious center came to be transferred from Fārs to Yazd and Kermān in which a group of Zoroastrians already lived, and from then onwards, these two provinces have always been home to the Zoroastrian community.
During the Safavid period, Shah Abbās transferred a number of Zoroastrians from Yazd and Kermān to Esfahān in order to avail of a cheap labor opportunity and made them settle in a place called “Gabrābād”. Some accounts of this place and the relatively comfortable lives of its dwellers have been recorded in the travel memoirs of some European travelers who had traveled to Iran and Esfahān during this period.
With the rise of Shah Abbās’s successors to power the persecution of the Zoroastrians gradually increased and reached to such an extent that Shah Soltān Hoseyn issued an order for all the Zoroastrians to abandon their religion and convert to Islam. Thereafter, a number of the Zoroastrians of Esfahān who had refused to submit to this command were massacred while some of them escaped to Yazd. The situation became still worse for the Zoroastrians when the invading Afghans attacked Kermān and destroyed “Gabrmahalleh” (lit.: “the Zoroastrian locality”), which was situated outside the fortification of the city and massacred its inhabitants. However, with the rise of Karim Khān Zand and the abolishment of the jizyah for the Zoroastrians of Kermān – who were being forced by the Afghans to pay the jizyah in compensation for all the Afghans who had been killed during their attack on Kermān – this community could spend some years in considerable peace.
During the Qājār rule and owing to the growing persecution of the Zoroastrians as well the economic pressures faced by them the number of this community reached an all-time low. This prompted the Parsis of India to dispatch a person called “Manekji Limji Hatāryā” to Iran as their reprehensive with a view to helping their religious fellowmen and improving their conditions. Hatāryā made some diligent efforts and after holding several rounds of talks with the Qajar king, Nāser al-Din Shah, and presenting him with numerous gifts succeeded in convincing the king to abolish the jizyah, allow the establishment of Zoroastrian schools and other educational centers, and to grant them certain freedoms. He also established an association for the Zoroastrians under the name “Anjoman-e Nāseri-ye Zartoshtiyān” (lit.” “The Naseri Association of Zoroastrians”). This association was first established in Yazd and then in Kermān and was in charge of managing the social affairs of the Zoroastrians as well as ensuring them with justice. As a result of these developments the living conditions of the Zoroastrian community of Iran gradually improved and this community succeeded in compensating for its earlier backwardness. Like the other religious minorities of Iran, the Constitution of the Islamic Republic of Iran recognizes the Zoroastrian community as one the Iranian religious minorities, and as per the clauses of the Constitution, the Zoroastrians, too, have their own separate representative in the Islamic Consultative Assembly (the Majles) of the country.
 Lajevardi , Fatemeh ” Iran Entry ” The Great Islamic Encyclopedia . Ed. Kazem Musavi Bojnourdi.Tehran: The Center of Great Islamic Encyclopaedia , 1989-, V.10 , pp.602 – 604