Levees are physical structures designed to prevent flooding by holding back water. Other terms that can be used to describe levees include barriers, embankments, dams, dikes, and flood walls. These synonyms all refer to the same basic concept, with slight variations in meaning. Barriers and flood walls both describe solid structures that prevent water from overflowing. Embankments and dikes are typically earthen walls or raised areas. Dams can also be used for flood control, but are usually designed for hydroelectric power generation. Whether referred to as levees, barriers, or embankments, these structures have been used since ancient times to protect communities and farmland from the damaging effects of flooding.