Newbury Castle is the name of an English castle built in 1152 by John Marshal during The Anarchy (A war in England and Normandy between 1135 and 1154). The location is thought to have been west of the town of Newbury.
The Castle is mentioned in the "L'Histoire de Guillaume le Marechal" (History of William the Marshall) wherein it describes King Stephen as besieging the castle for two months in 1153 and holding Marshal's son, William Marshal, as a hostage against Newbury's surrender. When the elder Marshal refused to comply, Stephen threatened to have the young boy catapulted over the walls. John responded defiantly, ‘I have the anvils and the hammer to forge still better sons’. King Stephen wasn't so heartless though as he relented and the boy survived.
Despite appearing proudly on the town's coat of arms, Newbury Castle does not appear to have been built in Newbury at all, but four miles (to the west) away in the village of Hampstead Marshall. There, the mottes of three castles can be found, which would be consistent with the general tactics of siege warfare during this medieval period without royal approval.
Today, there is little left to see at the site of Newbury Castle.