Akitu was the ancient Babylonian festival, lasting about twelve days, that celebrated the new year in spring.
Akitu was associated with the beginning of the agricultural year and was held in the month of Nisanu, corresponding roughly to March or April. It honored major Mesopotamian gods, especially Marduk in Babylon, and included processions, rituals, prayers, and the symbolic renewal of kingship.
One important setting was Babylon's Akitu house outside the city, connected to the main temple by a processional way. The festival's ceremonies helped reaffirm the proper order of the cosmos and the king's relationship with the deity.
Akitu is not the direct source of the modern January 1 holiday. Ancient societies used different calendars, and Babylonian new-year timing was tied to the lunar calendar and spring rather than the fixed Gregorian date used in many countries today.