Despite a long period of neglect, Gleaston Castle survives reasonably well and still retains significant remains of upstanding medieval fabric. It is a good example both of this class of monument, and of the type of military fortification which was constructed in northern England in response to a specific threat; in this case the border wars and Scottish raids of the 13th and 14th centuries.
The monument includes the upstanding and buried remains of Gleaston medieval enclosure castle. It is situated in a somewhat secluded location on the lower slopes of Beacon Hill about 0.5km north east of Gleaston village and immediately above the valley bottom through which Gleaston Beck flows. The castle consists of a quadrilateral enclosure surrounded by a stone curtain wall, and originally had strong square stone towers at each corner. These towers provided residential accommodation for the owners while the enclosed interior area would have been used for a range of purposes. Barracks, stables and workshops would have lined the inner side of the curtain wall but the absence of debris suggests that these buildings may have been of timber construction. The castle was built of limestone with some of the architectural features in red sandstone. The upstanding remains of the monument include the ruins of three of the four corner towers and substantial lengths of all but the northern curtain wall. The north western tower stands at the highest point of the castle. It is the largest of the four towers, and was built as a largely self-contained residence. Although considerably ruined, it measures c.28m by 16m and still stands up to 12m high. An entrance on the south side led into a spacious hall which was lighted on the south and flanked on either side by dungeons. Stone stairways led up to the living rooms on the first and second floors, with four apartments on each floor. A long passage in the north wall of the first floor communicates with a vertical shaft in the northern angle of the tower and indicates that the latrines were located at this corner on all floors. The surviving windows in this tower are narrow, but their sandstone quoins and heads have been more elaborately carved than elsewhere in the castle. In the west curtain wall immediately to the south of the north west tower there is a gateway, now blocked, which provided access into the castle yard. The west curtain runs south in a somewhat ruinous condition to connect with the south western tower. About halfway along the wall's length there is a ruined portion which projects westwards and which it is thought may mark the position of a demolished tower. South of this point, and adjacent to the south western tower, the curtain wall remains best preserved and measures up to 9m high by 2.7m thick. The now roofless south western tower is both the smallest in area and, at the same time, the highest of the four angle towers. It measures c.10m by 9.4m and stands c.19m high. A room on the ground floor is entered from the castle yard by a door 1m wide. The first floor, reached by a stone staircase in the east wall, has a fireplace and a couple of small narrow windows, and may have accommodated constables or officers of the manor, the dungeon below being a prison or store. The second floor is reached by exterior steps on the north side with an entrance door having a pointed arch of red sandstone, and is provided with a fireplace and two windows. The third floor is similar to the room below. The battlements are reached by a winding staircase in the north west angle, surmounted by a small watch turret. The three upper floors each have a small latrine built into the thickness of the south wall. Fragments survive of the south curtain wall which connects the south western and south eastern towers. The south eastern tower, which is also roofless, is a two storey building measuring c.13m by 9.5m and 12m high. Entrance is by a door having a pointed arch in the west wall which leads into a basement. There is a fireplace and two windows on the ground floor and a small latrine in the thickness of the wall. There was probably a cellar which appears to have been filled in with rubbish. Access was by a trap door in the floor. Access to the upper room is by a staircase in the west wall. This room contains a fireplace, four windows, and a latrine from which a doorway led out onto the south curtain wall. There is a spiral stair surmounted by a watch turret which gave access to the battlements. The east curtain wall connected the south eastern and north eastern towers. This latter tower is now merely a mound of rubble. The north curtain wall connected the north eastern and north western towers but this too has been demolished. Within the castle parts of the enclosure appear to have been artificially levelled and there are traces of earthworks which probably indicate the site of buildings such as barracks, stables and workshops. Construction of Gleaston Castle is thought to have commenced during the latter half of the 13th century under the ownership of Sir John de Harrington and at that time may have consisted of what is now the south west tower and the southern part of the west curtain wall, together with a possible tower at what is now the mid-point of the west curtain. This structure may have been irreparably damaged by the Scottish raids of 1316 for it appears that shortly after this time the curtain was repaired, extended and strengthened with towers at each corner. The north western tower was probably completed about 1340. In 1457 ownership of the castle fell by marriage to Lord Bonville of Shuton and the following year the castle ceased to be a manorial dwelling and thus quickly fell into disrepair. (Scheduling Report)
Ruins of castle. Probably early C14, abandoned late C15. Dressed stone with some ashlar dressings. Rectangular plan with rectangular towers to angles, 3 having substantial remains. No signs of wall to north, that to east now part of farm buildings. South-east tower has pointed entrance to west elevation some pointed windows to 1st floor, interior has stair within wall and ground floor and 1st floor fireplaces; remains of garderobe. South-west tower has steps to 1st floor entrance to north side, pointed lights; low undercroft, 1st and 2nd floor fireplaces and garderobes. Substantial remains of west wall, possibly had mid-wall tower; blocked entrance to north end adjoining north west tower, of which 3 parts remain, to north-west, south- west and east. Pointed windows remain, some with cusped ogee heads. Remains of mural passage and fireplace to north-west part. A manorial castle built for defensive purposes. (Listed Building Report)