Ancient Egypt was mostly mountains and deserts. But the people depended on agriculture for their food. Therefore a lot of effort went toward making sure that crops received enough water to thrive. Whi?

Egypt's crops were (and still largely are) dependent on the waters of the river Nile. Twice a year the Nile would flood its surrounding lands, depositing a layer of fertile silt. The ancient Egypians developed an elaborate irrigation system, using the Nile water to irrigate their fields.