A dike (or dyke) is an artificial earthen wall, constructed as a defense or as a boundary. It is also known in American English (notably in the Midwest) as a levee, from the French word levée (elevated). The best known form of dike is a construction built along the edge of a body of water, to prevent it from flooding onto an adjacent lowland. Dikes can be mainly found along the sea, where dunes are not strong enough, along rivers for protection against high-floods, along lakes or along polders. Furthermore, dikes have been built for the purpose of empoldering, or as a boundary for an inundation area. The latter can be a controlled inundation by the military or a measure to prevent inundation of a larger area surrounded by dikes. Dikes have also been built as field boundaries and as military defences. More on this type of dike can be found in the article on dry-stone walls.
Dikes can be permanent earthworks or emergency constructions (often of sandbags) built hastily in a flood emergency. When such an emergency bank is added on top of an existing dike it is known as a cradge.
