Redoubt Fortress

In 1803 Napoleon had subdued Italy and Austria and was preparing to invade Britain. He had assembled 167,000 men at Boulogne waiting for sufficient ships and barges to ferry them across the Channel.

In response to this threat the British Government began a massive building program to defend the south coast. 74 Martello Towers were built as well as three circular fortresses at Eastbourne, Dymchurch and Harwich.
Nelson’s victory over Napoleon at the Battle of Trafalgar in 1805 ended any risk that Britain could be invaded. By 1859 advances in warfare and artillery meant that a British Government report found that the Martello Towers and Redoubts were ‘not an important element of security against attack’. The Redoubt slowly fell into disuse.
http://www.eastbournemuseums.co.uk/RedoubtHistory.htm