A coastal fort built during the Napoleonic Wars is to be repaired to preserve it for future generations.

Martello Tower E, completed in Clacton-on-Sea in Essex in 1812, was constructed as part of a chain of 103 small coastal artillery forts to defend England from the threat of a French invasion.

Many of the forts have been lost to coastal erosion or demolished, with just 47 remaining, according to a survey, Historic England said.

Historic England has awarded a grant of £118,000 towards the repair of Martello Tower E, a Grade II-listed and scheduled monument, which has a leaking roof and an unstable and damp interior.

It was built behind a forward position battery, guard house and magazine which have long since disappeared.

According to a contemporary report, Martello Tower E was built to command “the landing place at Clacton Wash and the great road leading from it into the country”.

Its 33ft (10m) tall tower has walls up to 13ft (4m) thick, which are sloped inwards to resist cannon fire.

The open top floor carried three guns set on swivelling carriages, and the middle floor formed living quarters for about 25 men.

It was armed and provisioned but was never manned.

The War Office sold Martello Tower E to the West Clacton Estate in 1904, and by 1935 it lay within a Butlins holiday camp, which closed in the early 1980s.

Its roof was used to mount a cistern supplying water to the chalets at the holiday camp, which has since been replaced by housing developments.

Tony Calladine, regional director at Historic England in the East of England, said repair work is “urgently needed”, adding that the tower is a “striking visual reminder of Britain’s defence against the threat of invasion during the 19th century”.