The Sumerian King List, copied and recopied from the early second millennium BCE onward, frames the whole of Mesopotamian political history as a single institution passed between cities: "when kingship was lowered from heaven, kingship was in Eridu." The list treats individual dynasties as episodes within one continuous office rather than as separate inventions of rule, and it assigns implausibly long reigns to the earliest, most mythic kings before settling into historically plausible figures. The theological point outlasts the list's obvious legend: a Mesopotamian city did not simply produce its own ruler, it received one, and the gods could transfer that gift elsewhere if a king or his city failed them.
This framing gave kingship a religious job description before it gave the king a political one. He was expected to keep his city's temples in repair, to maintain the canals that fed its fields, to lead its army under the patron god's standard, and above all to render correct judgment, since justice was itself understood as a divine attribute the king held in trust. Royal inscriptions across two and a half thousand years of Mesopotamian history return to the same claims almost formulaically: chosen by the god, builder of the temple, shepherd of the people, restorer of just order after chaos. A king who failed at these tasks had not merely governed badly, he had broken the terms on which heaven had lowered kingship to his city in the first place, and Mesopotamian scribes were entirely capable of reading a dynasty's collapse as exactly that kind of theological verdict.