Martello towers, sometimes known simply as Martellos, are small defensive forts that were built across the British Empire during the 19th century, from the time of the French Revolutionary Wars onwards.
They stand up to 40 feet (12m) high (with two floors) and typically had a garrison of one officer and 15–25 men. Their round structure and thick walls of solid masonry made them 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 towers had moats or other batteries and works attached for extra defence.
The Martello towers were used during the first half of the 19th century, but became obsolete with the introduction of powerful rifled artillery. Many have survived to the present day, often preserved as historic monuments.
In the later half of the 19th century, there was another spate of tower and fort building, during the premiership of Lord Palmerston. These fortifications are therefore correctly called the Palmerston Forts, although, because they are circular in design, some confuse them with Martello towers.