Exterior of Martello tower, La Preneuse, Mauritius

A Martello tower at Clacton-on-sea on the East coast of England

An aerial view of a Martello tower

Martello towers are small defensive forts built by the British Empire at the time of the Napoleonic Wars. They stand about 40 feet (12m) high (with two floors) and had a garrison of one officer and 25 men. Their round structure and thick walls of solid masonry made them immensely resistant to cannon fire, while their height made them an ideal platform for a single heavy artillery piece, mounted on the flat roof and able to traverse a 360° arc. A few were surrounded by a moat for extra defence.

They took their inspiration (and their name, albeit mutated) from a round fortress at Mortella Point in Corsica. This had, in 1794, successfully beaten off the attack of two British warships, HMS Fortitude (74 guns) and HMS Juno (32 guns) but was eventually defeated by land-based forces after two days of heavy fighting. The British were duly impressed by the effectiveness of the tower against their most modern warships and copied the design. Between 1804 and 1812 they built a chain of similar structures to defend the south and east coast of England, Ireland and Guernsey to guard against possible invasion from France. 105 were built in England, set at intervals along the coast from Seaford, Sussex, to Aldeburgh, Suffolk. Most were constructed under the direction of General William Twiss (1745–1827) and a Captain Ford. 43 have survived in England, of which probably the finest is that at Dymchurch in Kent, which has been restored to its original condition.

The effectiveness of Martello towers was never actually tested in combat against a Napoleonic invasion fleet. Nonetheless, Martello towers were exported to many colonies of the British Empire.

One Martello tower, in Mauritius, nearby the La Preneuse public beach in Tamarin, has been restored by the Friends of the Environment and operates as a museum open for visitors. The original entrance to the tower is raised above ground, and a new entrance has been constructed at ground level.

Martello towers dot the Irish coast around Dublin Bay. Possibly the most famous of which is the Martello tower in Sandymount, in which James Joyce lived. Martello towers feature in many literary works based in the city.

Another Martello tower stands on the Plains of Abraham above Quebec City in Canada, overlooking the St Lawrence River. It has been restored as a museum and can be visited.

The last Martello tower built in the British Empire is said to be that at Fort Denison (http://www.ausemade.com.au/nsw/destination/f/fortdenison.htm), a small island in Sydney Harbour, New South Wales, for the protection of Sydney against possible attack by the Russians during the Crimean War. It is well preserved and a popular tourist attraction.

, List of fortifications, List of castles.