Which religion was officially supported by the Achaemenid Empire?

The religious identity of the Achaemenid Empire is a subject of ongoing scholarly debate, as there is no simple answer regarding an "official" state religion in the modern sense. However, the Achaemenid kings were closely associated with Ahura Mazda, the supreme deity of Zoroastrianism, and they frequently credited him with the success and legitimacy of their rule.1

While it is likely that kings such as Darius I, Xerxes I, and their successors were followers of an evolving form of Zoroastrianism, this faith had undergone significant development and syncretism since the time of the prophet Zoroaster. By the reign of Artaxerxes II, the royal religion had expanded to include the veneration of other ancient Iranian deities, such as Mithra and Anahita, alongside Ahura Mazda.1

It is important to note that the Achaemenid Empire was characterized by a policy of religious tolerance. The kings generally permitted conquered peoples to retain their own religions, customs, and local deities, as exemplified by Cyrus the Great’s approach to the Babylonians and the Jewish people.234