The Sumerian city-states were past the prehistorical period. History started with the invention of writing, and they did invent record keeping and writing. Now

The Sumerian city-states were past the prehistorical period. History started with the invention of writing, and they did invent record keeping and writing. Now it always possible to argue against the applicability of any rule, there are exceptions to rules. However here you would also need to give some argument, as to why this kind of reasoning could not be applied to this case. I could understand a community getting behind the construction of a water pipe, a place of worship (or even an operating system for personal computers). However a city wall is a slightly different kind of entity - this one is defining the boundaries of authority, it's a kind of us versus them entity.