Man-made island

An artificial island or man-made island is an island that has been constructed by people rather than formed by natural means. Artificial islands may vary in size from small islets reclaimed solely to support a single pillar of a building or structure, to those that support entire communities and cities.

Early artificial islands included floating structures in still waters, or wooden or megalithic structures erected in shallow waters (e.g., crannógs and Nan Madol discussed below). In modern times artificial islands are usually formed by land reclamation, but some are formed by the incidental isolation of an existing piece of land during canal construction (e.g. Donauinsel and Ko Kret), or flooding of valleys resulting in the tops of former knolls getting isolated by water (e.g. Barro Colorado Island). The largest artificial island, René-Levasseur Island, was formed by flooding of two adjacent reservoirs.

Despite a popular image of modernity, artificial islands actually have a long history in many parts of the world, dating back to the reclamed islands of Ancient Egyptian civilization, the Stilt crannogs of prehistoric Scotland and Ireland, the ceremonial centers of Nan Madol in the Micronesia and the still extant floating islands of Lake Titicaca. The city of Tenochtitlan, the Aztec predecessor of Mexico City that was home to 500,000 people when the Spaniards arrived, stood on a small natural island in Lake Texcoco that was surrounded by countless artificial chinamitl islands.

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