A crannóg is an artificial island or natural island, used for a settlement. They were found in Ireland and Scotland from around 3000 B.C. until around 1500 A.D.
The choice of an island as a home was mainly for defence purposes. Fish nearby would also have provided a convenient source of food.
The crannog could be reached from the nearest shore by means of a causeway built up with stones, or else a wooden gangway.