The reconstructed crannóg at Craggaunowen, Co. Clare.
A crannóg is an artificial or partly artificial island built in a lake. The name is derived from the Irish word Crann, a tree, and is used because of the large quantity of wood often used in crannóg construction. Typically a crannóg is an area enclosed by a circular palisade of upright timbers driven into the bed of the lake. The palisade was used to revet material, usually stone, peat, brushwood and timber that made up the platform. In some cases they were built on small islands. The houses were then constructed on the platform. The entrance to the crannóg is usually indicated by a gap in the palisade. A crannóg was usually approached by boat although the crannóg at Ballinderry 1, Co. Westmeath was connected to the shore by a brushwood causeway. There are about 2,000 known from Ireland that date from the Bronze Age to the medieval period. The crannóg at Ballinderry 2, Co. Westmeath was originally built in the Late Bronze Age and then rebuilt in the early medieval period. Some medieval sites like Lagore in Co. Meath are known to have been royal residences.