The beginning of the Babylonian year starts at the Spring Equinox. During Nisannu (Mar/Apr) of the Babylonian Calendar), the new moon after the equinox, the Akitu, the New Year Festival is held for twelve days. It starts with purifications and then the Enuma Elish (the Babylonian Creation Epic) is read. This myth begins with the original creation of the world by Tiamat, the God of Chaos, and Apsu, the God of Waters. Later Enlil, a God from the succeeding generation becomes the “Father of the Gods.” Eventually, He cedes his powers to Anu, from yet a newer generation of Gods, who seeks to overthrow the original Gods. After Apsu is killed, Tiamat wages war on the newer Gods. In desperation, Enlil goes to Marduk, the principal deity of Babylon, for help. On the condition that He is made the Ruler of the Gods, Marduk agrees. After killing Tiamat, Marduk remakes the world from her body.
During the Akitu, Marduk disappears. While his and Nabu’s temples are being cleansed, the people search for Him. At this time, they carry the statues of the other Gods to Marduk’s temple. Meanwhile, Nabu, the Scribe of the Gods and Marduk’s Minister, searches for and then frees Marduk from the Underworld. Then in his temple, the priests re-enthroned Marduk as the Ruler of the Gods. Afterwards, they do divination for the coming year. The festival ends with celebrations and the return of the Gods to their shrines.
Meanwhile to begin the growing season, the King would enact a sacred marriage with the temple priestess of Ishtar (Inanna). Their mating is to reaffirm the marriage of Ishtar, the Goddess of Fertility, with her husband, Tammuz (Dumuzi). These marriage rites ensure that the King is accepted as one of the Gods, and blessed by Ishtar, who also blesses the crops.
For Sumerians, the month is called Barazagar (Mar/Apr), the month of first offerings. The Akiti-Sekinku, the festival of harvesting barley, which starts at the full moon. For them, the month’s name – The Goddess of Barley Ashnan is honored as the “good bread of the whole world.”
Note: The Babylonians had a lunar calendar, and added months beyond the 12-month year. They kept their year keyed to the equinoxes. Between 1750 – 1500 BCE, they standardized their calendar – the Standard Mesopotamian Calendar to unify their empire.