Thetford Castle is a medieval motte and bailey castle in the market town of Thetford in the Breckland area of Norfolk, England. The first castle in Thetford, a probable 11th century Norman ringwork called Red Castle, was replaced in the 12th century by a much larger motte and bailey castle on the other side of the town. This new castle was largely destroyed in 1173 by Henry II, although the huge motte, the second largest man-made mound in England, remained intact.