The Redoubt was built between 1808 and 1810 to protect the port of Harwich against the threat of Napoleonic invasion. It was part of the scheme that included the construction of 29 Martello Towers on the East Anglian coast. The Redoubt is of circular shape, approximately 200ft in diameter, with a central parade ground of 85ft diameter. Hoists lifted shells from the lower level to the gun emplacements. It is similar in design to earlier redoubts at Dymchurch and Eastbourne.
Though difficult to imagine as it is now surrounded by houses, when the Redoubt was built it was on a hill top with free views in all directions. A house was demolished to make way for the Redoubt, and a large elm tree – used by ships as a navigational mark – was also removed. It is said that French prisoners of war were made to help in the construction.