A crannog is typically a partially or entirely artificial island, usually built in lakes and estuarine waters of Scotland, Wales, and Ireland. Unlike the prehistoric pile dwellings around the Alps, which were built on the shores and not inundated until later, crannogs were built in the water, thus forming artificial islands.

An artificial island is an island that has been constructed by humans rather than formed through natural processes. Other definitions may suggest that artificial islands are lands with the characteristics of human intervention in their format process, while others argue that artificial islands are created by expanding existing islets, constructing on existing reefs, or amalgamating several islets together. Although constructing artificial islands is not a modern phenomenon, there is no definite legal definition of it. 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. Archaeologists argue that such islands were created as far back as the Neolithic era. Early artificial islands included floating structures in still waters or wooden or megalithic structures erected in shallow waters.