In 529 B.C.E. Cyrus the Great came to power in the land of Persa (Greek Persis), a district on the south-western stretch of the Iranian plataeu on the Persian Gulf. He revolted against Cyaxares' son, Astyages, whose father had forged the mighty Median Empire; the capital of Media, Ecbatana , was taken, and the Median Empire in the flash of an eye became the Persian Empire. At first Nabonidus of Babylon hailed the victory, however, this soon changed as it was realized that the Persians would not honour any treaties that had been created previously betwixt the Medes and the various surrounding peoples. A coalition between Babylon, Egypt, Croesus, Lydia and Sparta faced the Persians. Croesus launched the first attack against the Persians in the spring of 546 B.C.E. - he was defeated in Pteria on the Cappadocian plane; Cyrus pursued him to Lydia. In the autumn of 546 B.C.E. Lydia fell. In 539 B.C.E. the Syrians, Babylonians, and Chaldaeans were defeated. Part of this swift victory can be accounted for new tactics ulitizing heavy bows that were implemented by the Persians - namely, to attempt not to come into hand-to-hand combat range with the enemy, but to instead, suffocate them in a hail of arrows as light cavalry armed with lances disrupted the enemy lines in small skirmishes. Also, the political dimensions of Mesapotamia and Asia Minor were such that once the Medes had been conquered, a vast range of territory could be instantly annexed under Persian rule; this was acheivable because few differences culturally and linguistically existed between the Persians and the Medes. Also, at this time the other kingdoms present in the region had been wearied by long warfare only half a century earlier; neither the Egyptians nor the Babylonians had the power to offset a powerful military move by the Persians once the Medes had fallen victim to the Persian bow.

Once Mesapotamia, Anatolia, and the southern Caucasus had fallen, the Persians were able to maintain a firm grip onto the empire for two reasons:

1) they conducted wars with great humanity.

The Kings of vanquished kingdoms were dealt with honourably and the towns of enemy kingdoms were always spared except for only in the gravest cases of insurrection. The members of conquered nationalities were welcomed under Persian service, both civil and military, where they would often stand side-by-side with the native Persian troops.

2) they were very tolerant of foreign religions.

Indeed, Cyrus the great, followed by his son Cambyses, and Darius I all were worshippers of Ahura-Mazda, however, it was obviously - as is seen in their tolerance of other religions and absence of conversion efforts - an impussiant adoration of the god, lacking the fervor of authentic Zoroastrianism; clearly, the Achaemenid kings followed a simpler and doctored Zoroastrian doctrine - it is known that, for instance, in the court of Xerxes, less that a hundred years later, the Zoroastrian faith had modified to such a degree that the cultic practice of Haoma, fervetly rejected by Zoroaster, was being practiced. Haoma we can trace back to ancient Aryan roots - it's counterpart in India is Soma; it is a ritualistic consumption of a plant extraction that would induce mild hallucinations; the exact nature of the extract is not known.

It is clear, at any rate, that the Achaemenids utilized religion rather as a political tool than a true descprition of their faith. It is clearly evinced, here, by the practices Cyrus the Great, his son, and Darius I employed within their conquered territories. For instance, one such particularly effective practice employed was to don the title of the local gods of any region conquered and then to parade in their name, maintaining the illusion that the former empire was still in place. In Egypt, the priestly class was even supported to continue with its ancient practices, and the building of new temples was funded. This all maintained a vast empire with varying cultures and religions quite successfully for a time. The Egyptians did revolt in 486 B.C.E. and were not subdued until Xerxes ascended the throne in 484 B.C.E. The Babylonians as well revolted in 484 B.C.E. and again in 479 B.C.E. only to be suppressed by Xerxes.

The Judeans were sufficietly fooled, however, and this is evident in statements in the books of Ezra and Nehemiah, where Cyrus the Great is described as having been filled with the will of the lord to come and aid in the building of the new temple, and also to return various artifacts having been exported by the babylonians during the Babylonian capitivity. The degree to which Zoroastrian beliefs influenced Judean religious beliefs can not be determined. Some argue the sect of the Pharisees derived it's name from "Farsi" the Iranian name for the district Parsa, which might indicate Zoroastrian preistly influence in the region, however, this can not be confirmed with certainty, although it is not impossible.

Now, eventhough the imperial court did not fervently seek conversion of their conquered territories to Zoroastrianism, the Zoroastrian faith did spread throughout the empire. It was particularly firmly rooted in Armenia (the southern Caucasus) and Cappadocia. This was, however, not the Zoroastrianism of Zarathustra, but a mutated version, influenced by Chaldaean astrology and magick as well as by other pagan traditions.