Harwich Redoubt Fort is a circular fortress built between 1808 and 1810 to defend the Essex port against Napoleonic invasion. This 180-foot-diameter fort features a dry moat and 8-foot-thick brick walls, containing 18 rooms for supplies, ammunition storage, and quarters for 300 soldiers. The fortress was armed with ten 24-pounder cannons and designed to withstand prolonged siege. Constructed with sufficient provisions and defensive features to maintain lengthy resistance, the fort is thought to have been built partly using French prisoners of war. Now operated by the Harwich Society and open to the public, it contains three small museums and hosts summer battle reenactments and historical events.
