Thetford Castle

The first castle at Thetford, known as Red Castle, was probably built shortly after the Norman Conquest by William de Warenne, Earl of Surrey, as a ringwork sited across the line of the town's Saxon defensive ditch, cutting the local church off from the town and building over part of its cemetery.

By 1100 the town was controlled by Roger Bigod, Earl of Norfolk, who raised a much larger motte-and-bailey castle on the other side of Thetford to guard the town and the crossing of the Icknield Way over the Thet and the Little Ouse. Its motte stood 19.6 metres high in a deep ditch, with a base 100 metres wide — the second-largest man-made mound in England — and local tradition holds much of its earth was quarried from the nearby Gallows Pits; raising it by hand is estimated to have taken around 24,000 man-days. The Bigods used Thetford together with their castles at Framlingham, Bungay and Walton to entrench their hold on East Anglia.

Roger's son Hugh Bigod took a prominent part in the Anarchy, rebelling against King Stephen from his East Anglian strongholds; a stone wall was probably added around the bailey around this time, and it has been suggested that a stone keep may also have stood there. When Henry II took the throne he moved to restore royal power, seizing Bigod's castles in 1157 — he later returned Framlingham and Bungay but kept Thetford for the crown.

Hugh Bigod then joined the revolt of Henry's sons, seizing the castle, but in 1173 Henry's forces retook it and slighted its fortifications; the motte itself proved effectively indestructible. Thetford was one of at least twenty rebel castles slighted in the revolt's aftermath.

The castle fell rapidly out of use after the 12th century, though the Castle Yard was still in use and said to have been surrounded by a stone wall as late as 1558. The east bank of the outer bailey was destroyed in 1772, and elm trees were planted near the top of the mound in 1823.

Its origins were meanwhile a matter of local legend and academic dispute: medieval tradition held that the devil had raised the mound after digging the dykes at Narborough and Newmarket, and other stories claimed it concealed a treasure-filled palace or six silver bells from Thetford Priory. Victorian antiquarians argued over a Celtic or Norman date before late-Victorian scholarship correctly settled on the Norman period; G. Knocker's 1957–58 excavation of Red Castle, and further fieldwork there by R. R. Clarke and Barbara Green in the early 1960s, established the design and date of that site.

The motte is now owned by the local authority as part of Castle Park, while the former bailey is known as Military Parade. The site is a scheduled monument.