Unlike Egypt, Iraq accommodated not one but two provincial identities, the Assyrian and the Babylonian. Both cultures had of course suffered violent destruction on their fall a thousand years before the Arab conquests as Nabopolassar and the Medes turned Assyria into heaps and ruins' in 612 B.C. so Xerxes razed the walls of Babylon, expropriated its citizens and turned its god into bullion after the revolt of 482. Both identities nonetheless survived, the first under a Christian aegis, the second under a pagan.
Th[e] unusual division of labour between Christianity and paganism was a result of the differing impact of foreign rule on the two provinces. Assyria, which had neither the fabled wealth nor the strategic importance of Babylon, had been left virtually alone by the Achaemenids and Seleucids; condemned to oblivion by the outside world, it could recollect its own glorious past in a certain tranquillity
. Consequently when the region came back into the focus of history under the Parthians, it was with an Assyrian, not a Persian let alone Greek, self-identification: the temple of Ashur was restored, the city was rebuilt, and an Assyrian successor state returned in the shape of the client kingdom of Adiabene. The Sasanids put an end to the autonomy of this kingdom, but they did not replace the local rulers with a Persian bureaucracy: though reduced to obedient servants of the Shahanshah, a native aristocracy therefore survived. Like the provincials of the west, the Assyrians stuck to their genealogy, but unlike them they could not merely go heretical: even a heretical Zoroastrian was still conceptually a Persian, and vis-a-vis the Persians the Assyrians therefore needed a different religion altogether. On the other hand, even an orthodox Christian was still only a Greek by association; vis-a-vis the Greeks a heresy therefore sufficed. Consequently, after a detour via Judaism, the Assyrians adopted Christianity and found their heresy in Nestorianism.
Babylonia, by contrast, had never been left alone. Apart from its massive Jewish diaspora, it was flooded with Persian immigrants under the Achaemenids, Greeks under the Seleucids and more Persians with the Sasanids; the latter built their capital there and in due course added yet another batch of foreigners in the form of Greek and Syrian prisoners of war. As a result the Babylonian polity was dissolved.
It is true that the ghost of Babylon haunted lower Iraq for some two centuries in the shape of the client kingdom of Mesene which, though founded by an Iranian satrap, soon went Aramaic; and there were no doubt other Aramean kings under the Parthians. But in the first place the Babylonian identification of Mesene was weak, and in the second place the Sasanid choice of lower Iraq as the centre of their empire hardly left much room for a native aristocracy, and whereas the Assyrians had a clear memory of their own past, the Babylonians did not. One might indeed have expected the Babylonian identity to vanish altogether, and if it did survive it was not because it remembered itself in isolation, but because it transcended itself and won universal respect: the Greeks bowed in deference to Babylonian astrology and borrowed it without disguising its Chaldean origin, and consequently the Chaldeans could borrow Greek philosophy without losing their identity. The fusion of Greek and Babylonian paganism generated a variety of astrological religions which, unlike the parent paganism, could hold their own against the supreme truths of Zoroastrianism, and which unlike Christianity were possessed of an ethnic label: an Assyrian had only an identity, a Christian had only a truth, but a Chaldean had both identity and truth. In Chaldea pagans therefore survived.
Christianity did, of course, spread to Babylonia; but whereas in Assyria it was a way of sanctifying a provincial identity, in Babylonia it was a way of desanctifying two. To the highly cosmopolitan environment of lower Iraq, Christianity, like Manichaeism, was a protest against ethnic religions, not a way of acquiring one: Manichaeism transcended the Chaldean and Persian truths by combining them as lesser insights within a larger and more grandiose scheme of things, and Christianity did the same by rejecting both as identical. The Christians of lower Iraq never lacked identity: they included Persians, Greeks, Elamites, Arameans, Qatraye, Arabs and others. Like the Assyrians, they might call themselves Suryane in contradistinction to the pagans; but they never shared any single identity between them: the only identity there was to inherit was Chaldean, and on conversion the Chaldean renounced his ethnicity as Magian and his culture as Zoroastrian. The Assyrian Christians have a genuine precedent for their name, but Christians were only called Chaldeans by way of abuse.