Barbara, Rosco, John and Kai, thanks for your insightful comments. I hadn't really expected this subject to attract much attention because this isn't what one might call a run of the mill topic. In fact it tends to be seen as academic (or nerdy if you will). It essentially falls in the realm of philosophy.
Most people don't pay enough attention to it but without these, any form of large scale civilized society is impossible. Without a system of shared beliefs, one cannot have groups larger than Dunbar's number, about 150 individuals where everyone personally knows everyone else and they are in universal conflict and rivalry with every other such group.
This is the exact description of the pre civilized hunter gatherer tribes and small agricultural settlements. They had their own witch doctor but nothing more universal than that. But when city states like Sumer, Babylon, Egypt and Mohenjodaro came about, these myths naturally came with them. It was the myths that gave rise to the city states, not the other way round. It's a huge cognitive revolution we fail to appreciate.