Religion in Iran has been shaped by multiple religions and sects over the course of the country's history. Zoroastrianism was the main followed religion during the Achaemenid Empire (550–330 BC), the Parthian Empire (247 BC – 224 AD), and the Sasanian Empire (224–651 AD). In 651 AD, the Rashidun Caliphate conquered Persia and spread Islam as the main religion. Sunnism was the predominant form of Islam before the devastating Mongol conquest, but subsequently, Shi'ism became eventually utterly dominant in all of Iran with the advent of the Safavids. According to the 2011 Iranian census, 99.98% of Iranians believe in Islam, while the rest of the population believe in other officially recognized minority religions: Christianity, Judaism and Zoroastrianism. Because irreligion and some other religions (including the Baháʼí Faith) are not recognized by the Iranian government, and because apostasy from Islam may be subject to capital punishment, governmental figures are likely to be distorted. A 2020 survey by the World Values Survey found that 96.6% of Iranians believe in Islam. On the other hand, another 2020 survey conducted online by an organization based outside of Iran found a much smaller percentage of Iranians identifying as Muslim (32.2% as Shia, 5.0% as Sunni, and 3.2% as Sufi), and a significant fraction not identifying with any organized religion - this shift is primarily the result of a backlash against more than forty years of theocracy (22.2% identifying as "None," and some others identifying as atheists, spiritual, agnostics, and secular humanists). According to the CIA World Factbook, around 90–95% of Iranian Muslims associate themselves with the Shia branch of Islam, the official state religion, and about 5–10% with the Sunni and Sufi branches of Islam. Christianity, Judaism and Zoroastrianism are officially recognized and protected, and have reserved seats in the Iranian parliament. Iran is home to the second largest Jewish community in the Muslim world and the Middle East. The two largest non-Muslim religious minorities in Iran are the followers of the Baháʼí Faith and Christianity. The Baháʼí community, historically is the largest religious minority group in Iran, has been persecuted during its existence and is not recognized as a faith. History Prehistory The first known religious traditions in Iran traditions developed over time into Zoroastrianism. Zoroastrianism The written Zoroastrian holy book, called the Avesta, dates back to between 600 and 1000 BC, but the traditions it is based on are more ancient. It was