Tynemouth Castle was originally a Norman earthwork motte and bailey fortress, founded by Robert de Mowbray. The castle is built on the site of an early Christian monastery, which was founded by Edward, the Saxon king of Northumbria, in 625. In 1085, a Benedictine priory was founded within the fortified enclosure and in 1296, King Edward I granted the priory a licence to crenellate. The Prior, founded the stone castle, when adding a continuous stone curtain wall, flanked by semi-circular towers, around the headland. In the 14th century, Prior John of Wethamstede strengthened the gateway, adding a three storey gatehouse, with an inner and outer barbican, behind a huge ditch.