To elaborate on what Foot wrote: I think we need to somehow declare the idea of Zoroastrianism as a strictly monotheistic religion defunct and obsolete; Even during the Sassanian dynasty where the "orthodox" Zoroastrianism (Which ironically was quite Hellenistic, especially per "Epiphanous" where the King of Kings became the "God Manifest" after the investiture had been completed, often after the reception of a sceptre or a diadem) was dominant, there was still a firm idea of dualism, the eternal struggle between Ahûrâ Mazdâ and Ahrîman, and a struggle of a divine army against that of the dêv/daevas, where manifestations of the sun (Mêhr/Mïhr/Mithras) and water (Ânâhîtâ/Anaïtis) and whatnot continue the struggle against their "moral privotations"; Zoroastrian cosmology pictures the spiritual world as a ziggurat, and as thus we may derive that the divine struggle manifests itself in several level, even into the "physical realm" of man, where the King of Kings would "fight against evil". Such imagery have perpetuated in the form of royalty engaging in the depicted killing of various beasts. Zoroastrianism and its connection to the pre-Zoroastrian polytheism has therefore been a complete absorption, with its own "Messiah" (Sâoshyant), "patron gods" (Who were the basis for the Zoroastrian calendar), such as Vahman (Patron of the good mind and conduct and guardian of the cattle), Verethragnâ/Varahrân/Vahrâm (Patron of war, struggle and victory), Sahrêwar/Shahrîvar (Patron of the metal) and so forth. The Zoroastrian religion is very closely knit to a popular mythology that somehow gave mankind and divinity a connection.
This form of divine duality is mirrored in the Levantine-originated Mandâëan doctrine, the Nasoraeans/Nasorites, which also portrays in its own way the function of the somewhat exclusive but very influential Zûrvân-sect of Mesopotamia, where the Chaldaeans added the fourth dimension, or a universe to encapsulate everything; Zûrvân existed in later Zoroastrianism as the "God of Time", but according to Zurvanism/Zervanism, Zûrvân is universal balance, or indeed, the universe. It is not hard to understand why the Chaldaeans who have an illustrious history as astrologers found such inclinations to be particularly appealing.
On one hand, it has been argued that Iranian kingship, especially with the advent of Cyrus II The Great of the Achaemenians, introduced proper secular rule (Richard N. Frye on the satrapal organization and its federalistic nature), bringing a sharp contrast to the popular perception of "direct Persian rule from eastern Scythia and India as far as Cyrene and Thrace", but on the other hand, Iranian royalty relied itself entirely, whether it be credit or legitimacy, upon religious institutions. It must have only been natural to surmise that the "King of Kings" and that the "leader of the good faith fighting against evil" must have been made legitimate only as the manifestation of God. Otherwise, he could never be fit to rule. This made the Iranian organization as a state a complex apparatus.
The Armenians during the Arsacid rule made only a slight modification to this rule, and in effect Zoroastrianism was merely replaced instead of Christianity. The feudal or federalistic organization was retained and the nakharars, and the azats kept their privileges, even during the Marzpanate era.
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