Nanna was the Sumerian moon god (not to be confused with the goddess Nanna, Baldr’s wife in Norse mythology). He later became identified with the Semitic god Sin. Nanna was said to be the son of Enlil and Ninlil. His wife, Ningal (Great Lady), bore him two powerful children, Utu/Shamash and Athtart/Inanna/Ishtar.
Nanna/Sin is called En-zu, meaning Lord of Wisdom, partially because the wisdom of astronomy and astrology depends on moon phases. From circa 2600-2400 BCE, when Nanna’s city of Ur controlled much of the Euphrates Valley, Nanna/Sin was head of the pantheon. He had a beard of lapis lazuli and rode a winged bull.
The important and entertaining Sumerian text Enlil and Ninlil tells how Nanna’s parents got together. It begins:
1-12 There was a city, there was a city — the one we live in. Nibru was the city, the one we live in. Dur-ĝišnimbar was the city, the one we live in. Id-sala is its holy river, Kar-ĝeština is its quay. Kar-asar is its quay where boats make fast. Pu-lal is its freshwater well. Id-nunbir-tum is its branching canal, and if one measures from there, its cultivated land is 50 sar each way. Enlil was one of its young men, and Ninlil was one its young women. Nun-bar-še-gunu was one of its wise old women.
13-21 At that time the maiden was advised by her own mother, Ninlil was advised by Nun-bar-ce-gunu: “The river is holy, woman! The river is holy — don’t bathe in it! Ninlil, don’t walk along the bank of the Id-nunbir-tum! His eye is bright, the lord’s eye is bright, he will look at you! The Great Mountain, Father Enlil — his eye is bright, he will look at you! The shepherd who decides all destinies — his eye is bright, he will look at you! Straight away he will want to have intercourse, he will want to kiss! He will be happy to pour lusty semen into the womb, and then he will leave you to it!”
But even Nun-bar-ce-gunu probably had no idea just how much lusty semen was going to be involved, as you’ll see if you read the story Enlil and Ninlil.
Here’s an interesting overview of Nanna and moon worship, from the book Myths of Babylonia and Assyria, by Donald A. Mackenzie:
Moon worship appears to have been as ancient as water worship, with which, as we have seen, it was closely associated. It was widely prevalent throughout Babylonia. The chief seat of the lunar deity, Nannar or Sin, was the ancient city of Ur, from which Abraham migrated to Harran, where the “Baal” (the lord) was also a moon god. Ur was situated in Sumer, in the south, between the west bank of the Euphrates and the low hills bordering the Arabian desert, and not far distant from sea-washed Eridu. No doubt, like that city, it had its origin at an exceedingly remote period. At any rate, the excavations conducted there have afforded proof that it flourished in the prehistoric period.
As in Arabia, Egypt, and throughout ancient Europe and elsewhere, the moon god of Sumeria was regarded as the “friend of man”. He controlled nature as a fertilizing agency; he caused grass, trees, and crops to grow; he increased flocks and herds, and gave human offspring. At Ur he was exalted above Ea as “the lord and prince of the gods, supreme in heaven, the Father of all”; he was also called “great Anu”, an indication that Anu, the sky god, had at one time a lunar character. The moon god was believed to be the father of the sun god: he was the “great steer with mighty horns and perfect limbs”.”
His name Sin is believed to be a corruption of “Zu-ena”, which signifies “knowledge lord”. Like the lunar Osiris of Egypt, he was apparently an instructor of mankind; the moon measured time and controlled the seasons; seeds were sown at a certain phase of the moon, and crops were ripened by the harvest moon. The mountains of Sinai and the desert of Sin are called after this deity.”
As Nannar, which Jastrow considers to be a variation of “Narnar”, the “light producer”, the moon god scattered darkness and reduced the terrors of night. His spirit inhabited the lunar stone, so that moon and stone worship were closely associated; it also entered trees and crops, so that moon worship linked with earth worship, as both linked with water worship.”
The consort of Nannar was Nin-Uruwa, “the lady of Ur”, who was also called Nin-gala. She links with Ishtar as Nin, as Isis of Egypt linked with other mother deities. The twin children of the moon were Mashu and Mashtu, a brother and sister, like the lunar girl and boy of Teutonic mythology immortalized in nursery rhymes as Jack and Jill.