Zoroastrians of the Indian subcontinent, namely the Parsis and Iranis, have not engaged in conversion since at least the 18th century. Zoroastrian high priests have historically opined there is no reason to not allow conversion which is also supported by the Revayats and other scripture though later priests have condemned these judgements. Within Iran, many of the beleaguered Zoroastrians have been also historically opposed or not practically concerned with the matter of conversion. Currently though, The Council of Tehran Mobeds (the highest ecclesiastical authority within Iran) endorses conversion but conversion from Islam to Zoroastrianism is illegal under the laws of the Islamic Republic of Iran. History Classical antiquity The roots of Zoroastrianism are thought to lie in a common prehistoric Indo-Iranian religious system dating back to the early 2nd millennium BCE. The prophet Zoroaster himself, though traditionally dated to the 6th century BCE, is thought by many modern historians to have been a reformer of the polytheistic Iranian religion who lived in the 10th century BCE. Zoroastrianism as a religion was not firmly established until several centuries later. Zoroastrianism enters recorded history in the mid-5th century BCE. Herodotus' The Histories (completed c. 440 BCE) includes a description of Greater Iranian society with what may be recognizably Zoroastrian features, including exposure of the dead. The Histories is a primary source of information on the early period of the Achaemenid era (648–330 BCE), in particular with respect to the role of the Magi. According to Herodotus, the Magi were the sixth tribe of the Medes (until the unification of the Persian empire under Cyrus the Great, all Iranians were referred to as "Mede" or "Mada" by the peoples of the Ancient World) and wielded considerable influence at the courts of the Median emperors. Following the unification of the Median and Persian empires in 550 BCE, Cyrus the Great and later his son Cambyses II curtailed the powers of the Magi after they had attempted to sow dissent following their loss of influence. In 522 BCE, the Magi revolted and set up a rival claimant to the throne. The usurper, pretending to be Cyrus' younger son Smerdis, took power shortly thereafter. Owing to the despotic rule of Cambyses and his long absence in Egypt, "the whole people, Persians, Medes and all the other nations" acknowledged the usurper, especially as he granted a remission of taxes for three years. Darius I and later Achaemenid