By the end of the 11th century there was a castle on the site consisting of earthen ramparts and a wooden stockade, but the priory was no longer in use. In 1296 the Prior of Tynemouth was granted royal permission to surround the monastery with walls of stone. In 1390 a gatehouse and barbican were added on the landward side of the castle. After the reformation in 1538 the monastic buildings were dismantled leaving only the church and the Prior's house. The castle, however, remained in royal hands. New artillery fortifications were built and the medieval castle walls were updated with new gunports. The church remained in use as a parish church until 1668 when a new church was built nearby. Beneath the ruins is the Oratory of St Mary or Percy Chapel. Its notable decorative features include a painted ceiling with numerous coats of arms and other symbols, stained-glass side windows, and a small rose window in the east wall above the altar. Much of the priory structure as well as the castle gatehouse and walls remain.