In the first half of the 16th century six blockhouses were built along the shore - from east to west they are Fisher's Nose, 2 either side of Millbay that have disappeared, Artillery Tower, Devils Point and Wilderness Point. A fort was also built on Drakes's Island. By 1596 the blockhouse at Fisher's Nose was supported by Plymouth Fort on the Hoe.
After the Civil War the most visible parts of the present defences were added, the Royal Citadel at the south of the city and, on the opposite shore, Mount Batten Tower.
In mid 18th century fortifications were built around Devonport dockyard. A number of earthwork batteries were also added around the northern end of The Sound. The defences were expanded at the end of the 18th century following concerns over possible French & Spanish invasions. This included Cavalier, Bluff, Stonehouse, Eastern King, Stonehouse, Mount Pleasant and Western King batteries. In the second half of the 19th century new defences were planned by Palmeston. 3 large forts were constructed - Staddon, Tregantle and Crownhill - supported by smaller forts including one on the breakwater Breakwater Fort - and batteries
In total, 70 batteries and forts have been built in the area around Plymouth, many of which are still standing and in use.
The first stone defences in Plymouth were those of the 15th century Plymouth Castle of which only a very small part of one tower remains near the Citadel. Previous to this the main local defences were at Plympton, but the importance of this castle faded as the River Plym silted up.