Fort Clarence is sited across St Margarets Street in Rochester, Kent. Work commenced in 1808 and completed in 1812 and was sited to prevent access from Maidstone Road to the River Medway. The work was composed of a long brick revetted dry ditch running between a fortified guardroom on the Maidstone Road to a similar tower alongside the Medway. The principal work (still surviving) is a massive red brick keep. The keep, looking like a medieval castle which served a dual role of gun tower and observation post. In the sides of the tower were embrasures to sweep the ditch with fire. St Margarets Street crossed the dry ditch by drawbridge through a substantial casemated guardhouse. From the tower ran a series of tunnels to the outlying guardhouses. Behind the dry ditch running from the tower down to Maidstone Road was a range of domestic building and barracks.

After 1815 the fort served a variety of different purposes. One use was as a military prison and lunatic asylum. After nearby Fort Pitt became a military hospital the patients were moved from Fort Clarence to a new purpose built asylum, although the prison remained with accounts of floggings being given in local newspapers. The fort was used by the garrison artillery throughout WWI as a recruiting centre. After the war a large TAVR centre was built alongside the site and the main barrack site run down. During WWII the Home Guard used Fort Clarence as local headquarters and with the invasion scare the fort was pressed into service again. During the war a massive underground aircraft factory was built under Fort Clarence for use by Short Brothers who had their main factory on the Medway below the fort.

After the was ended the Fort became derelict, then in the mid 1960s the GPO (now British Telecom) moved in, demolishing all the barracks, filling in a substantial part of the moat and demolishing the Maidstone Road guardhouse. The most substantial remains now are the brick gun tower and section of ditch from St Margarets Street into the next door public gardens. In the public gardens is a sally port with sealed up door. This connected with tunnel that led to the gun tower and probably to the Medway Tower, which is long demolished. Intruders into the tunnel system would have been greeted by fire from loopholes built into the entrance tunnels walls. The present status of the underground factory is unknown as the main entrance from the promenade has been built on and the factory that it served was demolished after Shorts left in 1949. The CAV company took over the factory until the late 1980s.

The site has now been converted to flats.