The political legitimacy of egyptian pharaohs, mesopotamian kings, and shang kings was closely tied to their perceived ability to use religious ritual and engineering to control one vital resource: water.
All the cities and civilizations were (and are) built near rivers or others water bodies. These people believed that the Gods controlled the seasons and other natural phenomena. They practised a lot of rituals to keep the Gods please so the conditions for living were optimal. The rulers led these rituals, as they ruled because of the grace of the Gods.
