Fall of Assur

The Fall of Assur occurred when the first city and old capital of the Neo-Assyrian Empire fell to Median led forces. The sack of the city that followed destroyed the city to some degree; however it recovered during the Achaemenid Empire and appears to have been a semi or fully independent Assyrian state during the Parthian Empire before being conquered by the Sassanids in the late 3rd century AD. The city remained occupied by Assyrians until the massacres of Tamurlane in the 14th century AD.
Background.
Ever since the end of Ashurbanipal's reign in 627 BC the Neo-Assyrian Empire was in an exposed and critical position; civil war, revolts in Babylonia, Anatolia, Caucasus and in the Levant coupled with Median, Babylonian and Scythian invasions proved too much for the empire torn by civil war. In 616 BC, the Babylonians established their "de facto" independence from the Assyrians.
Assault on the city.
In 615 BC, the Medes and their allies conquered Arrapha. The next year, they besieged Assur. Much of what was left of the Assyrian army was in Nineveh, unable to assist. Finally, after bloody hand-to-hand clashes (many skulls and skeletons were later found), the city was apparently taken in 614 BC.