The Mesopotamian civilization relied on two rivers: the Tigris and the Euphrates rivers. These rivers were the lifeline of the civilization as they provided water for irrigation, transportation, and many other needs. The Mesopotamian people were able to develop a sophisticated agricultural system by harnessing the water from the rivers, which allowed them to grow crops and sustain their settlements. The two rivers also played a crucial role in the development of trade and commerce, allowing for the exchange of goods and ideas between different settlements and civilizations. Overall, the Tigris and Euphrates rivers were essential to the survival and growth of the Mesopotamian civilization.