Creation of the World (Cosmogony)
In the beginning was not nothing, but water — and the gods who divided and named it.
Also: creation · cosmogony · creation of the world · Enuma Elish · Enuma Elish creation · separation of heaven and earth
Mesopotamian texts do not tell one creation story but several. Sumerian poems open with heaven (An) and earth (Ki) parted from a primeval unity, after which the gods set the world in order; the great Babylonian epic Enuma Elish has the god Marduk form sky and earth from the body of the slain sea-goddess Tiamat. Creation here is organization, not creation out of nothing: pre-existing waters and matter are shaped, named, and assigned their places. The emphasis falls on order, kingship among the gods, and the founding of cities and temples.
In short
The Mesopotamian accounts of how the ordered cosmos came to be, typically by the separation of heaven and earth and the organizing activity of the gods, rather than from nothing.
Where it’s found
Sumerian prologue of 'Gilgameš, Enkidu and the nether world' (ETCSL 1.8.1.4, in corpus); the Babylonian creation epic Enūma Eliš (akkadian-pending; ed. Lambert, Babylonian Creation Myths, 2013)
How the idea developed across Sumer, Babylon & Assyria
Sumerian cosmogonies (e.g. the prologue of 'Gilgameš, Enkidu and the nether world') open with the separation of heaven and earth and feature Enlil and the older gods; the Babylonian Enuma Elish (later, Akkadian) recenters cosmogony on Marduk and his defeat of Tiamat, a theological promotion of Babylon's city-god. Assyrian copies substitute Aššur for Marduk — the same myth re-skinned for a different capital.