Mesopotamia and Agriculture
It is interesting to contemplate the following progression:
Irrigation → high production farming → cities.
This is the story of Mesopotamia, the first substantial farming culture on earth. Its agricultural productivity supported the population density required for urbanism.
Before the settlements at Sumer, irrigation was developed in the steppe areas of Mesopotamia between the rivers and the Zagros Mountains. But there were limitations to productivity, including the supply of water and the characteristics of the soil. Men, in their crude knowledge of farming, had to rely on natural processes which were unpredictable.