Religion in the Achaemenid Empire was characterised by diverse religious cults and practices. The Achaemenid kings promoted the worship of Ahura Mazda but were tolerant of local beliefs. Within the wider Achaemenid empire, many Near Eastern cults existed, whereas the Persian heartland was characterized by a blend of Elamite and Iranian religious traditions.
One of the most debated topics in the scholarly community concerns the precise nature of the Mazda-worship by the Achaemenid kings. While there is an agreement among scholars that at least toward the end of the Achaemenid period, Zoroastrianism was the dominant religion, interpretations regarding the early kings can diverge substantially.
Sources Sources on the social, political and religious conditions of the Achaemenid Empire are mixed. On the one hand, the "Persians did not write historical accounts and preferred oral narratives." Direct evidence include the Achaemenid royal inscriptions, the Persian Fortification Tablets, the Elephantine papyri, as well as archeological evidence including the ruins of Persepolis, Susa and Pasargadae. External evidence is provided by a number of Greek authors.
Achaemenid royal inscriptions
The Achaemenid royal inscriptions present direct evidence of religious concepts and ideas of the early Achaemenid kings like Darius the Great and Xerxes. They show that they worshipped Ahura Mazda as their supreme god. In addition, starting with the reign of Artaxerxes II, the worship of Mithra and Anahita is promoted. Moreover, one inscription by Xerxes demonstrate that the Mazda-worship of the Achaemenids included a rejection of the daevas.
Persepolis Administrative Archives
The Persepolis Administrative Archives refers to administrative records of receipts, taxation, storage etc. They cover the area around Persepolis and contain records from 509 to 457 BCE. As a result, they provide a detailed snapshot of the economic conditions in the Achaemenid heartland during the time of the early kings.Stolper "What are the Persepolis Fortification Tablets?" The Oriental Institute News & Notes, 2007. Although they contain no direct references to religious ideas and concepts, some of them describe how food rations were provided for the performance of religious rituals. A detailed analysis by Henkelman has shown that most of the royal offerings were intended for the Elamite god Humban (see below), while other Iranian and non-Iranian gods are also mentioned. This demonstrates that while Ahura Mazda was of central importance to the self-identification of the Achaemenid kings, he was far less significant during this time to the general population in Persia proper.
Greek writers The Greeks began to write about Achaemenid Iran during the Persian Wars. Consequently, they were less interested in the religious landscape of their eastern neighbors and more in political and military aspects. If religious concepts are mentioned, Greek writers often employ the interpretatio graeca, by presenting the Persians as performing "Greek rituals for Greek divinities".
The earlierst source is Xanthus of Lydia, who wrote during the mid 5th century BCE. He lived in western Anatolia under Achaemenid rule. Of his work, however, only fragements have survived. The most important account is provided by Herodotus, who wrote shortly after Xanthus. During the 4th century BCE. more information on the religion of Achaemenid Iran become available. These works, however, have mostly survived as quotations only.
Iranian religions
The sources from the Achaemenid era demonstrate the worhip of a number of Iranian deities and the presence of Iranian religious concepts. However, connecting these sources to a specific religion, like Zoroastrianism, has been difficult. This is due to the fact that Zoroastrianism is derived from and consequently shares a number of features with those other traditions. There are very few sources on the Ancient Iranian religion but comparisons with the closely related Vedic religion from ancient India show a number of similarites. Such similarities include shared gods like Mithra (ved. Mitra), Airyaman (ved. Aryaman) and Apam Napat as well as religious concepts like Arta (ved. Ṛta), the chanting of manthras (ved. mantra) or the ritual consumption of haoma (ved. soma).
Moreover, even elements not found in the Vedic religion may be pan-Iranian religious innovations independent of Zoroastrianism. One example is Ahura Mazda, who is the supreme god of Zoroastrianism, but is completely absent from the Vedic texts. While scholars like Kreyenbroek therefore see him as a religious innovation of Zarathustra, others like Kuiper maintain that he was an early, pan-Iranian innovation independent of Zarathustra. A similar debate concerns the daevas, who are malevolent beings in Zoroastrianism, but are the regular gods of the Vedic pantheon.
Achaemenid kings
Due to the aforementioned problems, there is no consensus if the religious proclamations of the Achaemenid kings represent a form of Zoroastrianism or an independent Iranian religion with similar features. As a result, some scholars use the term Mazdaism as a placeholder for the otherwise unspecified religion of the (early) Achaemenid kings, whereas others reject this concept and use Mazdaism simply as a synonym for Zoroastrianism.
Proponents of a non-Zoroastrian interpretation of the Achaemenid inscriptions typically argue based on missing and misaligend elements in their incriptions and practices when compared to the Avesta, i.e., the normative collection of Zoroastrian texts. A missing element is, e.g., the total lack of Zarathustra's name in the Achaemenid inscriptions. Moreover, an often discussed misaligned element are the funerary practices of the Achaemenid kings. Since the Avesta mandates open-air excarnation, the Achaemenid practice of rock tombs like Naqsh-e Rostam has been used as evidence of a non-Zoroastrian ideology.
Zoroastrianism
There is substantial agreement among scholars that at least toward the end of the Achaemenid period, Zoroastrianism was the primary religion of both the Achaemenid kings and their priests, i.e, the Magi. This is based on two main rationals. First, Greek writers like Aristotle, Pseudo Plato or Theopompus - while writing in the 4th century BCE - explicitely state that the priests of the Achaemenids follow the teachings of Zoroaster (Zarathustra). Second, the Zoroastrian calendar is widely assumend to have been introduced sometime during the Achaemenid period.
However, opinions regarding the early kings (Cyrus the Great, Darius the Great, Xerxes) as well as when and why a transition to Zoroastrianism may have happened diverge substantially. Boyce for instance assumes that already Cyrus the Great followed Zoroastrianism, whereas Skjaervo assumes that at least from Darius the Great on they were Zoroastrians. Gershevitch opines that a conversion to Zoroastrianism happenend either under Darius the Great or Artaxerxes II. Malandra likewise assumes the reign of Artaxerxes II as the last possible date. Other scholars, however, remain agnostic.
More recently, a number of scholars have critized this discussion as being based on an essentialist and anachronistic understanding of early Zoroastrianism and its interaction with the religious landscape of the Ancient Near East. Stausberg for example notes that during the Achaemenid period, identity wasn't defined through religious creeds. Kreyenbroek has pointed out how in an oral religious tradition new ideas are interpreted and slowly synthesized inside an pre-existing mileu. Moreover, de Jong notes that the Avesta does not present a ready-made model for kingship and therefore highlights the ageny of the Achaemenid kings in creating and defining how they presented themselves. Finally, Skjaervø has argued that the assumption of a well-defined Zoroastrian orthodoxy during the Achaemenid period against which specific elements can be compared is elusive.
Proponents of a Zoroastrian interpretation have also countered criticism in a number of ways. First, they argue that the absence of Zarathustra's name is an argument from silence and point to the fact that his name is also missing in all official announcements of later Iranian dynasties. Morevover, Xanthus of Lydia - who wrote in the mid-5th century BCE - is quoted by Diogenes Laertius as saying that Zarathustra was the first of the Magi. Regarding the royal tombs, proponents of a Zoroastrian interpretation likewise point to the fact that all later Iranian dynasties used similar funeral practices, and that a number of their features can indeed be interpreted as an attempt to conform to Zoroastrian purity rules.
Moreover, proponents of a Zoroastrian interpretation highlight the general agreement between the main themes expressed in the royal inscriptions and the Avesta. Examples are the primacy of Ahura Mazda, the importance of Mithra and Anahita, the rejection of the daevas, the opposition between Good and Evil, the presentation of the Lie (drauga) as an active agent, as well as the so called Zitatnamen of the kings. In addition, they highlight several distinctively Zoroastrian features already connected to the Magi in the earlier sources, i.e., during the 5th century BCE. Examples are practices like Xwedodah, the killing of Xrafstar, open-air excarnation, as well as the veneration of Spenta Armaiti documented both in the Persepolis tablets and the Elephantine papyri.
Oxus
Oxus is an Iranian deity not known from the Avesta and, therefore, likely represents a non-Zoroastrian, Iranian religious tradition. The earliest textual evidence of the worship of Oxus, dated to the Achaemenid period, are personal names attested in Aramaic texts from Bactria from the fourth century BCE, such as Vaxšu-bandaka ("slave of Oxus" or "servant of Oxus"), Vaxšu-data ("created by Oxus") and Vaxšu-abra-data ("given by the clouds of Oxus"). Further examples occur in Hellenistic sources, for example Oxybazos ("strong through Oxus"), Oxydates ("given by Oxus"), Mithroaxos ("[given by] Mithra and Oxus") and possibly Oxyartes (if the translation "protected by Oxus" is accepted).
In Takht-i Sangin a temple dedicated to Oxus has been discovered. According to a number of Muslim geographers from the ninth and tenth centuries, this area was customarily considered the beginning of Jayhun (Oxus), which might constitute a survival of an originally Bactrian tradition responsible for the selection of this location as a cult center of the related river god. Excavations indicate that the temple was originally founded in the early Seleucid period, and remained in use until the reign of the Kushan king Huvishka. One of the objects from this site is a stone altar following Greek artistic conventions inscribed with a dedication of a certain Atrosokes to Oxus. His name is Bactrian and can be translated as "burning with sacred fire", and it is possible that he was a priest. Further excavations revealed three more similar Greek inscriptions, seemingly left behind by Bactrian worshipers of Oxus.
A seal with a human-headed bull from the Oxus Treasure is inscribed with Oxus' name written in the Aramaic script. It has been pointed out that the objects found in the temple of Oxus in Takht-i Sangin have close parallels among these belonging to the Oxus Treasure, which might indicate the latter was originally found in the same location. It has been suggested that priests of Oxus hid a number of objects out of fear of looting during a period of increased activity of the Yuezhi in the second half of the second century BCE, but failed to recover them, leaving the Oxus Treasure to only be discovered some two thousand years later.
Near Eastern religions
Elamite religion