Norwich Castle was founded by William the Conqueror some time between 1066 and 1075. It originally took the form of a motte and bailey. Early in 1067, William the Conqueror embarked on a campaign to subjugate East Anglia, and according to military historian R. Allen Brown it was probably around this time that the castle was founded. It was first recorded in 1075, when Ralph de Gael, Earl of Norfolk, rebelled against William the Conqueror and Norwich was held by his men. A siege was undertaken, but ended when the garrison secured promises that they would not be harmed.
Norwich is one of 48 castles mentioned in the Domesday Survey of 1086. Building a castle in a pre-existing settlement necessitated the destruction of existing properties. At Norwich, estimates vary that between 17 and 113 houses occupied the site of the castle. Excavations in the late 1970s discovered that the castle bailey was built over a Saxon cemetery. The historian Robert Liddiard remarks that "to glance at the urban landscape of Norwich, Durham or Lincoln is to be forcibly reminded of the impact of the Norman invasion". Until the construction of Orford Castle in the mid-12th century under Henry II, Norwich was the only major royal castle in East Anglia.
A mid-19th-century engraving of Norwich Castle from Charles Knight's Old England: A Pictorial Museum
The stone keep, which still stands today, was probably built between 1095 and 1110. In about the year 1100, the motte was made higher and the surrounding ditch deepened. During the Revolt of 1173–1174, in which Henry II's sons rebelled against him and started a civil war, Norwich Castle was put in a state of readiness. Hugh Bigod, 1st Earl of Norfolk was one of the more powerful earls who joined the revolt against Henry. With 318 Flemish soldiers that landed in England in May 1174, and 500 of his own men, Bigod advanced on Norwich Castle. They captured it and took fourteen prisoners who were held for ransom. When peace was restored later that year, Norwich was returned to royal control.
The Normans introduced the Jews to Norwich and they lived close to the castle. A cult was founded in Norwich in the wake of the murder of a young boy, William of Norwich, for which the Jews of the city were blamed. In Lent 1190, violence against Jews erupted in East Anglia and on 6 February (Shrove Tuesday) it spread to Norwich. Some fled to the safety of the castle, but those who did not were killed in their hundreds. The Pipe Rolls, records of royal expenditure, note that repairs were carried out at the castle in 1156–1158 and 1204–1205.
The castle was used as a prison for felons and debtors from 1220, with additional buildings constructed on the top of the motte next to the keep. The prison reformer John Howard visited it six times between 1774 and 1782. These buildings were demolished and rebuilt between 1789 and 1793 by Sir John Soane, and more alterations were made in 1820. The use of the castle as a gaol ended in 1887, when it was bought by the city of Norwich to be used as a museum. The conversion was undertaken by Edward Boardman and the museum opened in 1895.
The forebuilding attached to the keep was pulled down in 1825. Although the keep remains, its outer shell has been repaired repeatedly, most recently in 1835–9 by Anthony Salvin, with James Watson as mason using Bath stone. None of the inner or outer bailey buildings survive, and the original Norman bridge over the inner ditch was replaced in about the year 1825. During the renovation, the keep was completely refaced based faithfully on the original ornamentation.