The Akitu name and a seasonal temple festival go back to the third millennium BCE at Ur and other Sumerian cities, but the elaborate Babylonian program of royal humiliation, procession and recited creation epic is known in full detail only from first millennium sources, chiefly a set of ritual texts from the Seleucid era describing ceremonies attributed to earlier Neo-Babylonian practice. Assyriologists are divided on how much of the mature program existed in the second millennium versus how much was elaborated later around an older seasonal core, since the intervening textual record is thin. What is not disputed is the festival's political weight in its best attested form.
The Assyrian king Sennacherib, after sacking Babylon in 689 BCE, took Marduk's cult statue north to Assur specifically to disrupt the Babylonian Akitu, since without the god's image present in his own city the festival could not be performed as written, a calculated blow at Babylonian identity rather than mere plunder. The statue's eventual return decades later was itself treated as a restoration of cosmic and political order, underlining how tightly this single festival tied together kingship, city and cosmos in Mesopotamian religious thought.