Nanna or Sin was the god of the moon in Mesopotamian mythology.
Nanna is a Sumerian deity, the son of Enlil and Ninlil, and became
identified with Semitic Sin. The two chief seats of Nanna's/Sin's
worship were Ur in the south of Mesopotamia and Harran in the
north.
The original meaning of the name Nanna is unknown. The earliest
spelling found in Ur and Uruk is DLAK-32.NA (where NA is to be
understood as a phonetic complement). The name of Ur, spelled
LAK-32.UNUGKI=URIM2KI, is itself derived from the theonym, and
means "the abode (UNUG) of Nanna (LAK-32)".
The pre-classical sign LAK-32 later collapses with
ŠEŠ (the ideogram for "brother"), and the classical
Sumerian spelling is DŠEŠ.KI, with the phonetic
reading na-an-na. The technical term for the crescent moon could
also refer to the deity, DU4.SAKAR. Later, the name is spelled
logographically as DNANNA.
The Semitic moon god Su'en/Sin is in origin a separate deity from
Sumerian Nanna, but from the Akkadian Empire period the two undergo
syncretization and are identified. The occasional Assyrian spelling
of DNANNA-ar DSu'en-e is due to association with Akkadian
na-an-na-ru "illuminatior, lamp", an epitheton of the moon god. The
name of the Assyrian moon god Su'en/Sîn is usually spelled as
DEN.ZU, or simply with the numeral 30, DXXX.
He is commonly designated as En-zu, or "lord of wisdom." During the
period (c.2600-2400 BC) that Ur exercised a large measure of
supremacy over the Euphrates valley, Sin was naturally regarded as
the head of the pantheon. It is to this period that we must trace
such designations of Sin as "father of the gods", "chief of the
gods", "creator of all things", and the like. The "wisdom"
personified by the moon-god is likewise an expression of the
science of astrology, in which the observation of the moon's phases
is an important factor.
His wife was Ningal ("Great Lady"), who bore him Utu/Shamash
("Sun") and Inanna/Ishtar (the planet Venus). The tendency to
centralize the powers of the universe leads to the establishment of
the doctrine of a triad consisting of Sin/Nanna and his
children.
Sin had a beard made of lapis lazuli and rode on a winged bull. The
bull was one of his symbols, through his father, Enlil, "Bull of
Heaven", along with the crescent and the tripod (which may be a
lamp-stand). On cylinder seals, he is represented as an old man
with a flowing beard and the crescent symbol. In the
astral-theological system he is represented by the number 30 and
the moon. This number probably refers to the average number of days
(correctly around 29.53) in a lunar month, as measured between
successive new moons.
An important Sumerian text ("Enlil and Ninlil") tells of the
descent of Enlil and Ninlil, pregnant with Nanna/Suen, into the
underworld. There, three "substitutions" are given to allow the
ascent of Nanna/Suen. The story shows some similarities to the text
known as "The Descent of Inanna".
Nanna's chief sanctuary at Ur was named E-gish-shir-gal ("house of
the great light"). Sin had a sanctuary at Harran named E-khul-khul
("house of joys"). The cult of the moon-god spread to other
centers, so that temples to him are found in all the large cities
of Babylonia and Assyria. A sanctuary for Sin with Syriac
inscriptions invoking his name dating to the 2nd and 3rd centuries
CE was found at Sumatar Harabesi in the Tektek mountains, not far
from Harran and Edessa.