Mesopotamia, the land between the Tigris and Euphrates, home to Sumer, Akkad, Babylon, and Assyria, gave us the oldest religious literature that survives in the words of its own believers, because it was here that writing itself was invented. On clay tablets in cuneiform we can read, from the third and second millennia BCE, the myths, hymns, prayers, omens, and rituals of a civilization directly, the creation epic Enuma Elish, in which Marduk slays the chaos-mother Tiamat and builds the world from her body; the Epic of Gilgamesh, with its flood story and its meditation on mortality; the descent of Inanna/Ishtar into the underworld.
The Mesopotamian gods, Anu the sky, Enlil the storm, Ea/Enki the god of wisdom and the sweet waters, Inanna/Ishtar of love and war, were tied to particular cities and housed in temples atop great stepped ziggurats, and their cult centred on feeding and serving the gods so that they would maintain the order of the world. Mesopotamian religion also developed an elaborate science of divination, reading the future in the livers of sacrificed animals, in the movements of the planets (the origin of astrology and astronomy alike), and in dreams and omens. Its influence radiated outward: its flood story, its astral religion, and its underworld imagery all left deep marks on the Bible and on later Western thought. The region also remains the homeland of two living ancient faiths, Mandaeism and Yazidism.