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The Norman Age

After the Norman Conquest Thetford’s Priory and the castle (with the largest motte in England) were founded by Roger Bigod, a close friend of William the Conqueror.


During the eleventh and twelfth centuries the town of Thetford itself faced a period of economic decline after its Late Saxon heyday. However, the conquest of 1066 and the Norman dynasty founded by William the Conqueror had an important impact in Thetford; the town’s largest and most impressive medieval sites were created by the Normans.


The Domesday survey of 1086 recorded nearly 1000 burgesses living in Thetford, and although it is very difficult to work out full population figures from Domesday data, it has been suggested that the population of Thetford at the Conquest may have been around 4,500 people. This meant that Thetford was one of a handful of similar towns in England, on a par with Norwich, Oxford, Lincoln and York.

In 1071 the Bishop of East Anglia, Herfast, who had been newly appointed by William I, moved the see of East Anglia to Thetford, using the existing church of St Mary the Great as a cathedral. Herfast then built a new parish church, Holy Trinity, to replace St Mary. Herfast began to acquire wealthy manors and estates for the bishopric, and Domesday Book records the Bishop of Thetford, then William Beaufo, as holding over seventy manors across Norfolk. In 1094 the diocese was moved to Norwich, and the new bishop, Herbert de Losinga, began the construction of Norwich Cathedral.

Three major landowners were recorded in the Domesday Book in Thetford; the king, William the Conqueror, the Bishop, William Beaufo, and Roger Bigod. The population recorded in 1065 was around 4,500, but the Domesday survey suggests that by 1086 there were only 3,600 people living in Thetford; a decline of nearly a thousand people in the space of just twenty years. One of the reasons behind this decline was the rise in the fortunes of Bury St Edmunds, where the Abbot was granted extensive privileges over the surrounding area, including the suppression of markets outside Bury. Kings Lynn was also growing more prosperous during this period, so the importance of Thetford as a river port diminished.

Roger Bigod

Roger Bigod was to have a profound influence on the landscape of Thetford. He arrived in England with William the Conqueror and may have fought at the Battle of Hastings. The Domesday Book records that he owned a large amount of land in East Anglia, and he chose to make his base at Thetford.

In 1067-9 a castle was constructed in the ramparts of the Iron Age hill fort. The ramparts themselves were probably strengthened at the same time to form a bailey and a motte (artificial mound) was constructed at one end. The scale of the motte is enormous, at eighty metres high it is one of the largest in England. The size of the earthworks suggests that the castle was always intended to be a base of some importance in a strategically important urban centre. An excavation in the 1960s demonstrated that there were no buildings on top of the motte, and the castle was abandoned for military purposes after the twelfth century. The origins of the castle are unclear; it may have been constructed by Ralph Guader, who was Earl of East Anglia until his unsuccessful uprising in 1075, or it may have been raised by Roger Bigod who was created Earl after Guader. Bigod also constructed large castles at Bungay and Framlingham, both in Suffolk, and he may also have been responsible for Thetford.

Bigod also founded the Priory of St Mary in 1104, which became the largest and most important religious house in Thetford. The house was a Cluniac monastery, and the first monks came from Lewes in Sussex. The original site of the priory was south of the river at St Mary the Great (the former cathedral), but by 1107 the growing size of the community made a move to a larger site necessary, and the priory moved to its current site north of the river. The Priory is important as one of only three Cluniac foundations in Norfolk, and the scale and layout of the site is very similar to the contemporary priory at Castle Acre. The substantial remains of St Mary’s Priory, like Castle Acre, are managed by English Heritage and are open to the public.


Thetford Priory

Founded by Roger Bigod with substantial visible remains. Open to the public.

Thetford Castle

May have been built by Bigod, and also has impressive earthworks open to the public.

Red Castle

Earthworks of the ringwork castle are still visible.  The ringwork castle at Red Castle was constructed in around 1146, although excavations on the castle revealed that the site has a long history of occupation dating back to the Roman period. The castle was raised on top of the Late Saxon town defences and the site of a Late Saxon church, which may have been already disused by the mid twelfth century. Red Castle was sited to control the entrance to the town from the west, and the ford across the river at that location.


  • 1065 - Estimated population of 4,500

  • 1067-9 - Castle constructed within the ramparts of the Iron Age fort

  • 1071 - See of East Anglia moved to Thetford

  • 1086 - Population reduced to 3,600

  • 1094 - Diocese moved to Norwich

  • 1104 - Roger Bigod founds the Priory of St Mary

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