6th century BC Possible start of Zoroastrianism; however some date Zarathustra closer to 1000 BCE. Zoroastrianism flourished under the Persian emperors known as the Achaemenids. The emperors Darius (ruled 522–486 B.C.E.) and Xerxes (ruled 486–465 B.C.E.) made it the official religion of their empire.[20]