Hill forts are earthworks that are found in many parts of Britain and Ireland. They were built by the prehistoric inhabitants of the islands. Most of those still remaining date from about 200 B.C. The forts were placed at strategic points, generally on hilltops. They were built as circular walls of earth reinforced by fences made of tree trunks or stones and protected by deep ditches. They varied in size. Some had ditches and stockades (fences) to protect cattle, and pits and raised granaries for storing grain. Place names that include caer, dun, or burgh, or variants of these words indicate the site of a former fort. Examples are Caer Caradoc, Carlisle, Donegal, London, and Edinburgh (originally called Dun Edin).