Described as a 'fortified ecclesiastical' site by the Gatehouse website, the Grade I listed structure consists of a collection of 11th to 14th century buildings.
Above. Looking East across the Ouse towards Lindisfarne Castle.
It's likely that the cloisters were transformed into a fortified courtyard sometime in the 13th century, possibly due to the closeness of the castle to the East. During the 14th century, towers were added and an outer ward built. Also in the 14th century, the Priory church was lightly fortified with the insertion of arrow loops in the West wall, and the inclusion of crenelations.
The priory started out as a Benedictine cell from as early as 634AD, suitably removed from the mainland and accessible only via a causeway at low tide. The Priory was suppressed in 1547 during the English Reformation.
Information at England's North East web site.
Photo courtesy of Malcolm Booker