Immortality and Mortality of Mesopotamian Gods
“A further property of divinity was immortality. In narratives about divine deeds, gods were understood to be born of the intercourse of male and female parents. There is reference to their being nursed as infants but no further indication of a sense of their education, training or personal development.
Rather, as in the case of Marduk in the Babylonian Epic of Creation, the gods were born with full powers, knowing how to use weapons, understand magic words and so forth. As with Ninurta, a hero god, younger gods were expected to honour, obey and avenge slights to their parents. Having achieved a certain maturity, the gods stayed that way and did not age, though one and the same god could be portrayed as a youthful hero or as a sublime sage with magical, in preference to physical, prowess.
Gods could die, but only at the hands of other gods. Some died in battle or were executed for offences against higher gods. For example, the rebel god, Aw-ila, in the Story of the Flood (Foster 1996: 160–203 and below, pp. 184–5, 187) was executed to punish the uprising of the lesser gods against the great gods, but his spirit lingered on in the newly created human race, palpable as the human pulse. His flesh and blood were used to make the first human and his will may have given the human race its rebellious or wayward spirit.
The execution of Kingu, leader of the attacking army of gods and monsters in the Babylonian Epic of Creation, was modelled on this episode, but Kingu was there (falsely) accused of suborning Tiamat, mother of the gods, to kill her children (Foster 1996: 350–401).”
Benjamin R. Foster, “Birth and Death,” John R. Hinnells, ed., A Handbook of Ancient Religions, 2007, pp. 180-1.