The Sumerians lived along the Tigris and Euphrates Rivers in Mesopotamia, where the fertile soil and reliable water sources from seasonal floods supported agriculture. They developed irrigation canals and dams to control flooding, leaving a surplus of food that allowed specialization of labor into crafts and trade. The Sumerian cities were cut off from each other by desert, so they organized into independent city-states for political and economic purposes. Within the city-states, social classes divided people according to their occupations, with kings, priests, and warriors at the top. The Sumerians made important cultural contributions including the development of cuneiform writing and advances in areas like mathematics, astronomy, engineering, and