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.
Dikes were first constructed in the Indus Valley Civilization (in Pakistan and North India from circa 2600 BC) on which the agrarian life of the Harappan peoples depended.
The modern word dike is most probably derived from the Netherlands "dijk", where the construction of dikes is well attested since the 12th century. The 126 km long Westfriese Omringdijk, for instance, was completed by 1250, and was formed by connecting existing older dikes. The Roman chronicler Tacitus however mentions the fact that the rebellious Batavi pierced dikes to flood their land and to protect their retreat (AD 70). The Dutch word dijk meant originally both the trench or the bank. The word is closely related to the English verb to dig (EWN).
In Anglo-Saxon, the word dic already existed and was pronounced with a hard c in northern England and as ditch in the south. Similar to Dutch, the English origins of the word lie in digging a trench and forming the upcast soil into a bank alongside it. This practice has meant that the name may be given to either the excavation or the bank. Thus Offa's Dyke is a combined structure and Car Dyke is a trench though it once had raised banks as well. In the midlands and north of England, a dike is what a ditch is in the south, a property boundary marker or small drainage channel. Where it carries a stream, it may be called a running dike as in Rippingale Running Dike, which leads water from the catchwater drain, Car Dyke, to the South Forty Foot Drain in Lincolnshire (TF1427). The Weir Dike is a soak dike in Bourne North Fen, near Twenty and alongside the River Glen.
Dikes are very common on the flatlands bordering the Bay of Fundy in New Brunswick and Nova Scotia Canada. The Acadians who settled the area can be credited with construction of most of the dikes in the area, created for the purpose of farming the fertile tidal flatlands. These dikes are referred to as "aboiteau".
A dike made from stones laid in horizontal rows with a bed of thin turf between each of them is known as a spetchel.
Dike can also mean a pond in the same way as Australians use the word dam. However, this is more likely in the several other languages which use obviously related words. Frisian is one of them. The Frisians who settled in England with the Angles and Saxons form a linguistic link with Dutch dating from well before the 12th century. See the stories of Saints Boniface and Wulfram.
In April 2006, South Korea completed the Saemangeum Seawall, displacing the Afsluitdijk as the longest man-made dike in the world.
