The post-imperial period was the final stage of ancient Assyrian history, covering the history of the Assyrian heartland from the fall of the Neo-Assyrian Empire in 609 BC to the final sack and destruction of Assur, Assyria's ancient religious capital, by the Sasanian Empire AD 240. There was no independent Assyrian state during this time, with Assur and other Assyrian cities instead falling under the control of the successive Median (615–549 BC), Neo-Babylonian (612–539 BC), Achaemenid (539–330 BC), Seleucid (312– 141 BC) and Parthian ( 141 BC–AD 224) empires. The period was marked by the continuance of ancient Assyrian culture, traditions and religion, despite the lack of an Assyrian kingdom. The ancient Assyrian dialect of the Akkadian language went extinct however, completely replaced by Aramaic by the 5th century BC.

During the fall of Assyria in the Medo-Babylonian conquest of the Assyrian Empire 626–609 BC, northern Mesopotamia was extensively sacked and destroyed by Median and Babylonian forces. The Babylonian kings, who annexed large parts of Assyria cared little for economically or socially developing the region and as such there was a dramatic decline in population density. Many of the greatest cities of the Neo-Assyrian period, such as Nineveh, were deserted and others, such as Assur, decreased dramatically in size and population. The region only began the process of recovery under the rule of the Achaemenid Empire. After his conquest of Babylon in 539, the Achaemenid king Cyrus the Great returned the cult statue of the Assyrian national deity Ashur to Assur. The Achaemenid practice of not interfering with local cultures, and the organization of the Assyrian lands into a single province, Athura, allowed Assyrian culture to endure.

Assyria was extensively resettled during the Seleucid and Parthian periods. In the last two centuries or so of Parthian rule, Assyria flourished; the great cities of old, such as Assur, Nineveh and Nimrud were resettled and expanded, old villages rebuilt and new settlements constructed. The population density of Parthian Assyria reached heights not seen since the Neo-Assyrian Empire. Much of Assyria was not ruled directly by the Parthians, but instead by a number of vassal kingdoms, such as Hatra and Adiabene, which had some Assyrian cultural influence. Assur, at this time at least two thirds of the size the city was during Neo-Assyrian times, appears to have been a semi-autonomous city-state, governed by a sequence of Assyrian city-lords who might have seen themselves as the successors of the ancient Assyrian kings. This latter-day Assyrian cultural golden age came to an end when Ardashir I of the Sasanian Empire overthrew the Parthians and, during his campaigns against them, extensively sacked Assyria and its cities.

Terminology The centuries that followed the fall of the Neo-Assyrian Empire are characterized by a distinct lack of surviving sources from Assyria. The textual and archaeological evidence is so scant that the period is often referred to as a "dark age" or simply called "post-Assyrian". Because Assyria continued to be viewed by its inhabitants and by foreigners as a distinct cultural and geographical entity, and (though never again fully independent) continued to at times be administrated separately, modern scholars prefer the name "post-imperial" for the period.Frahm, Eckart (2023). "Assyria's Legacy on the Ground". Assyria: The Rise and Fall of the World's First Empire. Basic Books. p. 353. .

History Neo-Babylonian rule

The fall of the Neo-Assyrian Empire after its final war with the Neo-Babylonian and Median empires dramatically changed the geopolitics of the Ancient Near East; Babylonia experienced an unprecedented time of prosperity and growth, trade routes were redrawn and the economical organization and political power of the entire region was restructured. It has long been disputed whether Assyria, or at least its northernmost portions along the Taurus Mountains, fell under the control of the Medes or the Babylonians, but sources are not unanimous and the situation is difficult to reconstruct.

Archaeological surveys of northern Mesopotamia have consistently shown that there was a dramatic decrease in the size and number of inhabited sites in Assyria during the Neo-Babylonian period, suggesting a significant societal breakdown in the region. Archaeological evidence suggests that the former Assyrian capital cities, such as Assur, Nimrud and Nineveh, were nearly completely abandoned. Some cities had been completely destroyed by the Medes and Babylonians in the war; the level of destruction and the sacking of Assyria's temples is described with horror and remorse in some of the contemporary Babylonian chronicles. The breakdown in society does not necessarily reflect an enormous drop in population; it is clear that the region became less rich and less densely populated, but it is also clear that Assyria was not entirely uninhabited, nor poor in any real sense. Many smaller settlements were probably abandoned due to the local agricultural organization being destroyed over the decades of war and unrest. Many Assyrians are likely to have died in the war with the Medes and Babylonians or due to its indirect consequences (i.e. dying of disease or starvation) and many probably moved from the region, or where forcefully deported, to Babylonia or elsewhere. Large portions of the remaining Assyrian populace might have turned to nomadism due to the collapse of the local settlements and economy.

Although the Neo-Babylonian kings largely kept the administration of the Assyrian Empire and at times drew on Assyrian rhetoric and symbols for legitimacy, particularly in the reign of Nabonidus (556–539 BC, the last Neo-Babylonian king), they also at times worked to distance themselves from the Assyrian kings that had preceded them and never assumed the title 'king of Assyria'. Throughout the time of the Neo-Babylonian and Achaemenid empires, Assyria was a marginal and sparsely populated region, perhaps chiefly due to the limited interest of the Neo-Babylonian kings to invest resources into its economic and societal development. Individuals with Assyrian names are attested at multiple sites in Babylonia during the Neo-Babylonian Empire, including Babylon, Nippur, Uruk, Sippar, Dilbat and Borsippa. The Assyrians in Uruk apparently continued to exist as a community until the reign of the Achaemenid king Cambyses II (530–522 BC) and were closely linked to a local cult dedicated to the Assyrian national deity Ashur.

Though it is clear that recovery was slow and the evidence is scant, there was at least some continuity in administrative and governmental structures even within the former Assyrian heartland itself. At some point after the fall of Nineveh in 612 BC some of the faces in the reliefs of its palaces were destroyed, but there is no evidence for longer Babylonian or Median occupation of the site. At Dur-Katlimmu, one of the largest settlements along the Khabur river, a large Assyrian palace, dubbed the "Red House" by archaeologists, continued to be used in Neo-Babylonian times, with cuneiform records there being written by people with Assyrian names, in Assyrian style, though dated to the reigns of the early Neo-Babylonian kings. Two Neo-Babylonian texts discovered at the city of Sippar in Babylonia attest to there being royally appointed governors at both Assur and Guzana, another Assyrian site in the north. The cult statue of Ashur, stolen from Assur during its sack in 614, was however never returned by the Babylonians and was instead kept in the Esagila temple in Babylon. At some other sites, work was slower. Arbela is attested as a thriving city, but only very late in the Neo-Babylonian period, and there were no attempts to revive the city of Arrapha until the reign of Neriglissar (560–556 BC), who returned a cult statue to the site. Harran was revitalized, with its great temple dedicated to the lunar god Sîn being rebuilt under Nabonidus. Nabonidus's fascination with Harran and Sîn have led modern researchers to speculate that he himself, a usurper genealogically unconnected to earlier Babylonian kings, was of Assyrian ancestry and originated from Harran. Nabonidus did go to some length to revive Assyrian symbols, such as wearing a wrapped cloak in his depictions, absent in those of other Babylonian kings but present in Assyrian art. Some Assyriologists, such as Stephen Herbert Langdon and Stephanie Dalley, have also gone as far as to suggest that he was a descendant of the Sargonid dynasty, Assyria's final ruling dynasty, as a grandson of either Esarhaddon (681–669 BC) or Ashurbanipal (669–631 BC), though this is disputed given the lack of strong evidence.

Achaemenid rule

The Persians first entered Assyrian territory in 547 BC, when the founder of the Achaemenid Empire, Cyrus the Great, crossed the Tigris river and marched south of Arbela while campaigning against the Medes. Assyria probably came under Achaemenid control in late 539, shortly after Cyrus conquered Babylon in October. Under the Achaemenids, most of Assyria was organized into the province Athura (Aθūrā), but some was incorporated into the satrapy of Media (Mada). The organization of most of Assyria into the single administrative unit Athura effectively kept the region on the map as a distinct political entity throughout the time of Achaemenid rule. In Achaemenid inscriptions on the royal tombs of the kings, Athura is consistently mentioned as one of the empire's provinces, next to, but distinct from, Babylonia. Some of the Achaemenid tombs depict the Assyrians as one of the ethnic groups of the empire, alongside the others. The Achaemenid kings interfered little with the internal affairs of their individual provinces as long as tribute and taxes were continuously provided, which allowed Assyrian culture and customs to survive under Persian rule. After the Achaemenid conquest, the inhabitants of Assur even received the permission of Cyrus the Great to at last rebuild the city's ancient temple dedicated to Ashur and Cyrus even returned Ashur's cult statue from Babylon. Cult statues might also have been returned to Nineveh, though the relevant inscription is damaged and could refer to another city. Just as during the Neo-Assyrian Empire, the lingua franca of the Achaemenid Empire was Aramaic. By this time, the Aramaic script was often referred to as the "Assyrian script".

It is not known how Athura was organized internally. An Aramaic letter sent by the governor of Egypt in the late 5th century BC attests to the presence of Achaemenid officials at the cities of Arbela, Lair, Arzuhin and Matalubaš, which suggests that there was a certain level of administrative organization in the region. At Tell ed-Daim, located on the Little Zab northeast of Kirkuk, an Achaemenid administrative building of substantial size (), probably a palace of a local governor or official, has been excavated.