[3] An area of reclaimed land, formerly part of the Pevensey tidal lagoon but now marshland and fields crossed by the Eastbourne to Hastings railway line, is situated immediately to the south of the castle.

[7] An impression of its original appearance can be gleaned from an area in the north wall which has been excavated down to the still-intact foundations, revealing how it was once faced on both sides with small blocks of stone.

[12] Because the fort was partly surrounded by marshes and water, which provided natural defences, the Romans economised by only building towers on the more vulnerable north-eastern and far western sectors.

A ditch bisected the causeway, which led up to a rectangular gatehouse with a single arch around 2.4 metres (7 ft 10 in) wide, with a D-shaped tower on each end from which archers could fire along the archway.

[5] The interior of the fort was artificially raised by the Romans, using earth dug from the foundation ditch, to bring it up to the level of the projecting step on the back of the wall.

A wooden bridge around 20.7 metres (68 ft) long linked the inner and outer baileys, though the cost of maintaining it prompted its replacement in 1405 with a stone causeway and drawbridge pit that can still be seen today.

It was subjected to systematic stone-robbing for centuries; as early as 1591, it was recorded that all the best stones had been "imbeselled and carried away" and that one family had removed no fewer than 677 cartloads of ashlar facing-stone from the keep's walls.

The interior of the curtain wall was lined with timber-framed domestic buildings such as the great hall, which appears to have been totally rebuilt by Edward I in 1301–02 and possibly on other occasions.

The fort is named as Anderitum, apparently meaning "great ford", in the Notitia Dignitatum, a list of Roman "dignities" (i.e. public offices) as of the 5th century.

Like the other Saxon Shore forts, Anderitum's position at a strategic harbour would have enabled the Romans to control access to the shoreline and prevent invaders from penetrating inland.

It is not known whether their name is a geographical or functional one but their description by Zosimus suggests that they were an elite body of troops, who served both in the field army and, probably in the form of a single detachment, at Anderitum.

According to the Anglo-Saxon Chronicle, in 477 a Saxon raid drove local people into the forest of Andreadsleag (which from another reference seems to have stretched over 200 kilometres (120 mi) from the mouth of the River Lympne to Hampshire).

[5] Although the history of the fort at this time is unrecorded, archaeological evidence indicates that its inhabitants had wide-ranging trade links that enabled them to import wares from as far afield as Macedonia and Syria.

[45] Anderitum had fallen into ruin by the time of the Norman Conquest of England but it still remained a formidable fortification in a very strategic location, offering a natural anchorage near one of the narrowest points of the English Channel.

[46] When William the Conqueror launched his invasion of England by landing at Pevensey Bay on 28 September 1066, his army sheltered for the night in a temporary fortification situated within the old Roman fort.

He followed a similar pattern elsewhere in England, building the Tower of London alongside the still-extant Roman city wall and constructing Colchester Castle on top of the ruins of the Temple of Claudius.

He also appears to have used the site to distribute lands to his Norman followers, with Pevensey Castle and the surrounding Rape of Penvensey being gifted to his half-brother Robert, Count of Mortain.

Defeated members of the royalist army fled to Pevensey, pursued by de Montford's forces, but the garrison refused an invitation to surrender and endured over a year of besiegement.

[61] However, it continued to play a significant role in the defence of the south coast against French raids and was occupied through much of the 14th century by a garrison consisting of between twenty and thirty men.

The Duke of Lancaster, John of Gaunt, refused to garrison it in 1377 five years after he took possession of the castle, asserting that he was wealthy enough to rebuild it if a French attack destroyed it.

His actions attracted public hostility which culminated during the Peasants' Revolt of 1381 when a mob attacked the castle, burnt its court rolls and abused the steward.

[63] In a letter sent to Bolingbroke, Pelham wrote: My dear Lord ... if it please you to know of my affairs, I am here bylaid in manner of a siege, with the counties of Sussex, Surrey and a great part of Kent, so that I may not out, nor no vitals get me without much difficulty.

Its inmates included King James I of Scotland, who was captured while en route to France in 1405, and Edward of Norwich, 2nd Duke of York, who was held at Pevensey after becoming involved in a plot against Henry IV.

It was nearly demolished during the period of the English Commonwealth in the 17th century when Oliver Cromwell's Parliamentary Commissioners sold it for £40 to a builder, John Warr of Westminster, who planned to quarry it for its stones.

[70] In 1925 its last private owner, the 9th Duke of Devonshire, gave the castle to the state as a historic monument and it underwent repairs and some reconstruction under the supervision of the Ministry of Works.

[71] It acquired a fresh military significance in 1940 when Pevensey's exposed shoreline and flat hinterland became a possible target area for a German invasion after the fall of France.

The first recorded excavation on the site took place in 1710, when the vicar of Pevensey sought to dig a channel from the castle's moat, within the outer bailey, to convey water to the village.

This revealed how the wall had been constructed, resting on a foundation of rubble-packed oak piles and beams which were described as exhibiting "no symptoms of decay, and even the leaves of some brushwood which had been thrown in were found equally well preserved.

[75] Six years later, two antiquarians, Mark Antony Lower and Charles Roach Smith, were granted permission by the Duke of Devonshire to carry out an excavation of the castle with the support of sponsors and the London, Brighton and South Coast Railway, which provided free transport.

In 1993–95, a team from the University of Reading led by Professor Michael Fulford carried out a series of excavations in the area of the keep and on the Roman fortress's east side.