Sumerian cities were protected by

They built walls around their cities for protection

Explanation:

Sargon the Great

Around 2,300 BC, the independent city-states of Sumer were conquered by a man called Sargon the Great of Akkad, who had once ruled the city-state of Kish. Sargon was an Akkadian, a Semitic group of desert nomads who eventually settled in Mesopotamia just north of Sumer.

Sumer City-States

Explanation:

They built walls around their cities for protection. Farmland was outside the walls, but people would retreat to the city when invaders came.

food chain i would say only because there is competition on getting food and survival

what is the question