In later times, "the king assumed the identity of the god while the high priestess seems to have embodied the goddess. Such a rites appears also to have formed part of the Nanna cult. We know that the high priestess of Nanna in Ur, chosen from the royal family (of which Enheduanna, daughter of Babylonian King Sargon, is most famous -M), was considered to be the human spouse of the god. .. Her title, zirru, is a name for Ningal (spouse of Nanna -M) so she may well have been the embodiment of the goddess. One may guess that the sacred marriage was celebrated at the Akitu festival of Nanna in the twelfth month, when offerings connected with "setting up the bed" were recorded." (Treasures of Darkness" Thorkild Jacobsen, 125-126)
Offerings to Nanna were agricultural, as we see in "Nanna's Journey to Nippur". "It tells how Nanna decided to go to Nippur to visit his father and loads his boat with all kinds of wood and animals. On the journey upriver from Ur he passes several major cities at each of which the tutelary goddess comes out to greet and bless him. Eventually he reaches Nippur where he tells the doorkeeper of Enlil's temple to open: he has come to feed the herds and flocks, to fill the basket with birds' eggs, to look after the reeds of the marshes, bring wild pigs and various fishes. He is also going to get myriad ewes with lamb, letting the rams in among them, myriad goats with kid, letting the bucks in among them, and myriad cows with calf, letting the bulls in among them. The gatekeeper joyfully opens the gate and Enlil, delighting in his son, prepares a treat for him. He calls for cakes such as Nanna loves, bread, and he has beer poured for him --all agricultural rather than herding delicacies-- and in addition he gives him general prosperity to take back with him to Ur: carp-flood in the rivers, grain in the fields, fishes in the rivers, reeds in the marshes, plants in the high desert, harts in the forests, and long life in the palace.
"The myth of Nanna's Journey to Nippur is closely connected with the spring rite of the ninsag-boat (its name means "first fruits boat") which took gifts of the first dairy products of the year from Ur to Nippur. The meaning of this ritual act, we would suggest, was religious celebration and sanction of the exchange of products of the different economies of the cattlemen in the southern marshes and of the farmers in the north." (Treasures of Darkness" Thorkild Jacobsen, 126-127)
"Nanna seems to refer to him specifically as the full moon. Suén as the crescent, and yet a third name, Ašim-babbar, as the new light." (Treasures of Darkness" Thorkild Jacobsen, page 121. )
The Mesopotamians were aware of the difference between the lengths of the lunar and solar years, and eventually the moon (the god Nanna in Sumerian and Sîn in Akkadian) achieved dominance over the sun (the god Utu in Sumerian and Shamash in Akkadian) as the determiner over the year: "[Nanna], fixing the month and the new moon, [setting] the year in its place." The importance of the moon for determining the length of the year was noted by Rim-Sin, the ruler of Larsa, who praised the moon as: "Nanna, who establishes the months, who completes the year." The Sumerians perception of the superiority of the moon was reflected also in their mythology wherein the moon was considered the father of the sun. The supremacy of the moon was evident in the year being measured by the complete lunar cycles. Even those annual festivals whose annual existences were bound to the solar seasons were assigned fixed days in an irrelevant lunar schema. But as an acknowledgement of the unbreakable bond between the solar year and its religious festivals, the Mesopotamians intercalated the year to insure that festivals observed in a particular month with the seasonal phenomena being celebrated. (The Cultic Calendars of the Ancient Near East, Mark E. Cohen, page 3)
First-born son of Enlil, typically referred to as 'Father Nanna' as his full noon slowly moved across the nighttime sky. His cosmic functions were to light up the night, measure time, and provide fertility.
"Corresponding to the phases of the moon, festivals called ešeš ()i.e., 'all-temple" or "general" festivals) were celebrated on the first, seventh, and fifteenth during the Third Dynasty of Ur." (Treasures of Darkness" Thorkild Jacobsen, 122)
The moon god Sîn. Detail from a cylinder seal of the Neo-Babylonian period.