|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.|
In the first half of the 16th century six blockhouses were built along the shore. A fort was constructed in the 1580's on Drake's Island and in 1596 Plymouth Fort was built on the Hoe. After the Civil War the most visible parts of the present defences were added, the Royal Citadel between 1665 and 1670 at the south of the city on the upper part of the site of Plymouth Fort and Mount Batten Tower on the opposite shore in the 1650's.
In the middle of the 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. In the second half of the 19th century new defences were planned by Palmerston. Ten large land forts were constructed, Staddon & Stamford to the east, Tregantle & Scraesdon to the west and six, including Crownhill, to the north. These were supported by gun batteries protecting Cawsand Bay and Penlee Point, plus one on the breakwater, Breakwater Fort.
In total, 70 batteries and forts have been built in the area around Plymouth, many of which are still standing.