The new year and Akitu festivals in Babylonia were celebrated in the spring, during which the high priest of Marduk’s Esagil temple would read the Babylonian creation story, Enuma Elish. This narrative tells how the young god Marduk became king of the gods by saving them from Tiamat and her army of monsters.A good overview of the Akitu Festival and the Enuma Elish.
For more on the Enuma Elish, see here. For more on the ancient Akitu Festival, which has been connected with both Rosh HaShanah and Yom Kippur, see here and links. As that post notes, the ancient Babylonian festival has been revived and is celebrated annually in the spring by Assyrian Christians.
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