The historic town of Wallingford lies within an earth rampart first thrown up in the reign of Alfred the Great or Edward the Elder, as a precaution against Danish attack. Wallingford was once believed to be a Roman town because the rampart encloses a rectangular area and the streets follow a grid pattern. The rampart can still be followed on the three landward sides but there is no evidence of any man-made defenses facing the river. In the Norman period the rampart was heightened, but the town then fell into economic decline so the timber stockades that lined the summit were never replaced in stone.
The northeast quarter of the town enclosure became the site of Wallingford Castle. William the Conqueror crossed the Thames here in 1066, during his march on London, and he may have founded the castle in passing. It certainly existed by 1071. This important royal fortress fell into the Empress Matilda's hands during the Anarchy and resisted King Stephen in three great sieges. The platform of a siege fort from this time can be seen across the river.
The castle showed its strength again in the Civil War. It resisted the might of Parliament until July 1646 - virtually the end of the war - and even then surrendered honorably. Six years later it was destroyed as a potentially dangerous stronghold. The earthworks comprising a large motte between two baileys are still quite impressive but almost all the masonry has disappeared.
A number of English kings contributed to the defenses, notably Henry II and John, resulting in an impressive castle with a shell keep on the motte and two towered curtains. A section of the outer rampart has been turned into a public garden and this carries an excavated length of wall and one round tower. Castle House now occupies the inner bailey.