When people first moved into the region between the Tigris and Euphrates, they found living pretty easy. There was wildlife to catch, fish in the rivers, and edible vegetation growing wild. So they stayed.
Soon they found that they could grow their own food if they tended the land. Then they figured out how to get river water into the fields, and crops grew in abundance. Other tribes saw the wealth and food the people of the river valleys had, and started raiding to take it. So to protect themselves, they started building walls around their town. Cities grew from these towns.
The Sumerians had gardens shaded by tall date palms where they grew peas, beans and lentils, vegetables like cucumbers, leeks, lettuces and garlic, and fruit such as grapes, apples, melons and figs.
A money economy begin to replace the barter economy in the high middle ages because : B. as trade expanded to cover greater distances, a unit of exchange became more important
