Occupying a commanding position at the head of Portsmouth Harbour, in the medieval period Portchester was an important port.

In anticipation of a French invasion during the first quarter of the 14th century, Edward II spent £1,100 repairing and reinforcing Portchester Castle.

[7] Although the Roman army retreated from Britain in the early 5th century, it is unlikely that the fort was ever completely abandoned, although its use continued on a much smaller scale.

In 904, Portchester came into the possession of King Edward the Elder and the fort became a burh to help defend the country against Vikings, as listed in the Burghal Hidage.

At this point it would probably have been defended by a wooden palisade and a moat, with the original Roman stone walls of the fort acting as the defence of the outer bailey.

He died in 1120, and a few years later the family estates came into the hands of William Pont de l'Arche through marriage to Robert Maudit's daughter.

[10] William Pont de l'Arche probably retained possession of Portchester Castle until his death in 1148, although who inherited it is uncertain.

When Henry II's sons rebelled against him with the support of some leading barons in the Revolt of 1173–1174, Portchester was made ready for war.

[14] Louis' campaign was initially successful and he captured London and Winchester before Portchester Castle surrendered to his forces in June 1216.

[15] Henry tried to recapture Normandy, which was lost by his predecessor, until conditions in England forced him to abandon them in 1259, and Portchester was a frequent departure point for troops on campaign.

Despite the expensive work undertaken by Edward II, a survey of 1335 recorded that many of the castle's buildings were in a ruinous state, and the south wall of the Roman fort had been damaged by the sea.

Although he infrequently stayed at Portchester,[17] in June 1346 Edward III assembled his 15,000 strong army there before leaving for France on the campaign that ended in victory at the Battle of Crécy.

Between 1396 and 1399 the royal apartments that stand today, albeit in a ruined state, were built for Richard II under master mason Walter Walton.

[19] In 1415, King Henry V was making preparations at Portchester Castle for a campaign in France, part of the Hundred Years' War between the two countries.

[21] In the 15th century the nearby town of Portsmouth some six miles (ten kilometres) away grew to become a significant economic centre and an important port.

Despite its state, when Margaret of Anjou, wife of Henry VI, landed in England in 1445, Portchester Castle was selected as her port of arrival.

When Henry VIII visited with Queen Anne Boleyn in 1535 October, it was the first time in over a century that the reigning monarch had been to the castle.

With relations with Spain worsening, Elizabeth I made Portchester Castle ready for war, anticipating a Spanish invasion.

A royal survey from 1609 documents the castle's improved condition, noting that the buildings built by Cornwallis contained "four fair lodging chambers above and as many rooms for office below".

The castle is a popular venue for school outings, while the sea wall is frequented at high tide by anglers in pursuit of flounder and bass.