Rivers in Mesopotamia like the Tigris and Euphrates supported early civilizations through providing fertile soil and aiding trade and travel. The flooding of the rivers was both beneficial, leaving rich soil, and problematic, being unpredictable. Farmers learned to control the flooding through dams and irrigation channels. Key achievements of the Mesopotamians included inventing the wheel, developing the cuneiform writing system, plow, and advances in math including a number system and calendar.