Martello towers are gun towers constructed to defend the vulnerable south eastern coast of England against the threat of ship-borne invasion by Napoleonic forces. Built as a systematic chain of defence in two phases, between 1805-1810 along the coasts of East Sussex and Kent, and between 1808- 1812 along the coasts of Essex and Suffolk, the design of martello towers was based on a fortified tower at Mortella Point in Corsica which had put up a prolonged resistance to British forces in 1793.
Martello tower no 66 survives well, and retains a substantial proportion of its original components and associated features, including its original gun barrel, which is a rare survival amongst martello towers. As one of the surviving examples of a series of low-lying towers, no 66 also provides a significant insight into the strategic integration of the martello tower system. Recognition of its structural and strategic strengths during the 20th century, against a new invasion threat, is represented by the addition of a substantial gun emplacement during World War II.