The earthwork, rock cut and some of the earth covered parts of the Royal Commission fort known as Crownhill Fort, built between 1863 and 1872. Part of a series of defences which protected the city of Plymouth and Devonport Dockyard from attack by land. The fort was designed by Captain EF Du Cane as the principal and largest fort of the defensive line, and lie between Woodland Fort and Bowden Battery, to which it was connected by a military road.This is an outstanding example of the later period Royal Commission fortifications and is the only one of this type in Plymouth to be actively preserved and open to the public. A earthen rampart measuring from 20 metres to 30 metres wide surrounds the fort, which has an irregular septagonal plan. It is accessed via a single storey, stone gatehouse to the south. Within the fort is a large semicircular parade ground surrounded by buildings, including officers quarters, barracks, a magazine and a cookhouse. The survival of numerous slit trenches and foxholes of World War II date provide evidence for the forts later history.