Zoroastrianism in Iran
Zoroastrianism is considered to be the oldest religion still practiced in Iran. It is an Iranian religion that emerged around the 2nd millennium BCE, spread through the Iranian plateau, and eventually gained official status under the Achaemenid Empire in the 6th century BCE. It remained the Iranian state religion until the 7th century CE, when the Arab conquest of Persia resulted in the fall of the Sasanian Empire to the nascent Rashidun Caliphate.