If the beginning of the historical period is marked by the invention of writing, mythology in the historical period probably began in Mesopotamia in the Sumerian culture. This is not to say that orally transmitted myths did not exist before they were captured in writing.

Scholars generally believe that the Sumerians invented writing in the mid- to late-fourth-millennium B.C.E. The system used—called cuneiform script—involved the carving of pictographs and later phonemes into clay tablets. Lists of Sumerian gods and fragments of the great Gilgamesh epic have been found on such tablets. According to the Sumerians, a semi-divine hero-king named Enmerkar invented writing when, at war, he found that a messenger—“his mouth heavy”—could not repeat a complicated message exactly. His only recourse was to create picture words on a tablet.