Thetford is a market town and civil parish in the Breckland District of Norfolk, England. It is on the A11 road between Norwich and London, just east of Thetford Forest. The civil parish, covering an area of , in 2011 had a population of 24,340. There has been a settlement at Thetford since the Iron Age, and parts of the town predate the Norman Conquest; Thetford Castle was established shortly thereafter. Roger Bigod founded the Cluniac Priory of St Mary in 1104, which became the largest and most important religious institution in Thetford. The town was badly hit by the Dissolution of the Monasteries, including the castle's destruction, but was rebuilt in 1574 when Elizabeth I established a town charter. After World War II, Thetford became an "overspill town", taking people from London, as a result of which its population increased substantially. Thetford railway station is served by the Breckland line and is one of the best surviving pieces of 19th-century railway architecture in East Anglia. The origin of the name Thetford is unclear. The site was an important crossing of the River Little Ouse, so one possibility is that the settlement drew its name from the Anglo-Saxon Theodford or people's ford. It is also unclear if the nearby River Thet is named after the crossing or the later settlement. Breckland was used as an excavation site for flint tools around 2000BC. During the Iron Age, a fort was established on Icknield Way at the site of Thetford Castle. Thetford was an important tribal centre for the Iceni during the late Iron Age and early Roman period, with Castle Hill and Gallows Hill being sites of particular note. During the Saxon period it was the principal centre of the eastern Heptarchy and a regular battle site between locals and the Viking invaders. A mint was built in Thetford in the 9th century. A monastery was established around 1020 and a grammar school was operating since before the Norman Conquest of 1066. The town greatly prospered during the reign of Edward the Confessor (1042–1066), and at one point there were 944 free Burgesses living in Thetford.