The first record of a dam was from the Greek historian Herodotus. The dam was built across the Nile River in about 2900 B.C. to protect the city of Memphis from flooding. Dams were popular with the Romans, and two of their dams are still in use today, almost 2000 years later. Dam construction was mostly lost after the Romans until the 1800's.
Dams can serve many different purposes.
A dam can be either a storage, diversion, or detention dam. Storage dams are built to trap water so that it can be used later, for example, an artificial reservoir to provide a city with drinking water. Diversion dams are often used for irrigation. Detention dams are constructed to either stop or slow the amount of water in a river. This is mostly to prevent flooding.