Fort Borstal was built as an afterthought from the 1859 Royal Commission on the Defence of the United Kingdom, by convict labour. Construction started in 1875 but was suspended in 1885. The fort was completed around 1895. it was one of a series of four forts that ringed Chatham.
Fort Borstal was designed to hold the high ground southwest of Rochester, South East England. It is of polygonal design and was not originally armed. An anti-aircraft battery was based there in the Second World War.
A gauge railway was built connecting the four Chatham ring forts of Borstal, Bridgewoods, Horsted and Luton. A rope-worked incline led west from Fort Borstal down to a gravel pit and wharf on the River Medway. About of track remains intact at Fort Borstal.