Situated on a promontory on the east coast of Portsea Island, Fort Cumberland has evolved over the centuries to meet the defensive needs of the day. Commanding the entrance to Langstone Harbour, the first known fort to occupy the site was probably built during Tudor times in the reign of Henry VIII.

After the fall of the Jacobites at Culloden in 1745, and the subsequent escape of 'Bonnie Prince Charlie' across the channel, a new threat from France became a real possibility. As a consequence, the victorious Duke of Cumberland gave orders for a new fort to be constructed on the site in 1747. The fort was star-shaped in form, and constructed mainly from earth. Behind an earthen Glacis (low-inclined sloping rampart), there was a dry moat with rampart and parapet protecting a central courtyard. Within the courtyard, a guardhouse, storeroom, powder magazine and barrack block were located.

When a further threat from France in 1785 was perceived, the Duke of Richmond argued for extensive rebuilding of the Portsmouth defences, including Fort Cumberland. The new fort would be a much larger affair, built using brick and stone, and taking the regular form of a pentagon enclosing a central courtyard. At each of the five points of the 'star', a diamond-shaped bastion was constructed and, beyond this, a dry moat and Glacis with a Ravelin block to the west. Building work took a considerable time, and the fort was not completed until about 1812. Covering an area of some 24 acres, this was the first fort in Britain to provide casemated ordnance.

In all, there are 74 casemates surrounding the courtyard, but the current condition of each varies. Within the courtyard itself are two pair of semi-detached houses, as well as a range of ancillary buildings and workshops. In the early 1860s, Fort Cumberland's ordnance was upgraded from smooth bore to rifle muzzle loading (RML) guns. Major alterations to three of the five bastions were made during the period 1886-1892 to accommodate further advances in ordnance, and by 1892 the fort was equipped with 3 x 6 inch (150mm) rifle breech loading (RBL), 2 x 9 inch (225mm) RMLs and 1 x 64 pounder.

Fort Cumberland provided the base for The Royal Marine Artillery between 1823 and 1971. The fort saw little action during its 200 year history, with the exception of a German bombing raid on Portsmouth in 1940. This not only caused considerable structural damage, but cost the lives of eight Royal Marines.

In 1964 Fort Cumberland was scheduled an ancient monument, and received a Grade II listing in 1969. It was taken into the guardianship of English Heritage in 1975.

Probably the finest surviving 18th century fort of its type in Europe, Fort Cumberland today serves as the base for English Heritage's 'Centre for Archaeology'. Unfortunately, it is only open to the public for pre-booked guided tours, or specific heritage open days, but it is well worth taking the opportunity for a visit.