The monument consists of the remains of a palace which was a residence of the Bishop’s of St David’s during the medieval period. The origins of the palace are likely to be pre-Norman; the place name Lamphey derives from the Welsh Llandyfái , ‘church of St Tyfái’, however the earliest certain reference to a bishop’s residence, concerning the siege of Pembroke Castle in 1096, is in relation to Bishop Wilfred (1085-1115). At that time it is likely buildings would have been of timber. The earliest masonry at Lamphey is from an early 13th century hall, slightly earlier than another replacement building added to its west side. Both buildings faced north into a precinct that was probably protected by a boundary wall and gatehouse. During the episcopy of Bishop Henry de Gower (1328-47) a prolonged period of construction resulted in new hall on the south east as well as other buildings within the precinct. Further changes, the remodelling of existing buildings and the construction of a new chapel took place shortly after 1500, before the manor was surrendered at the Reformation. The palace was the home of the Devereux family for a short time in the late 16th century. By the eighteenth century the buildings had been abandoned and parts had been converted into farm buildings. The precinct was cleared and converted into a walled garden in the nineteenth century to serve the new house of Lamphey Court to the north. In 1925 the palace was placed in state care.
The first hall is now largely ruinous, it comprised a hall and service rooms set above an undercroft, the entrance was by external stair and door on the north side. The building added to the west, probably a replacement built for Bishop Richard Carew (1256-80) survives well, the hall was also at first-floor level, entered through a richly-carved door on the north. The original 13th-century ornate lancet windows are visible inside, though altered in the early 16th century when square-headed windows were inserted. The interior retains a decorated fireplace, and painted plaster survives on a window in the south-east corner. The south side has a small projection which housed the latrine. The new, larger hall built by Bishop Henry de Gower was constructed at a slight angle to the rest of the buildings on the south east and surmounted with a less ornate form of the arcaded parapet that he had overseen built at St. David’s cathedral. Above a vaulted ground-floor undercroft an external fight of stone steps on the north leads to the single undivided great hall on the first floor with six windows of two-trefoiled lights. A projecting wing on the south contained latrines. In front of these buildings were two courtyards. A larger outer precinct, entered through a gatehouse on the west and an inner courtyard the wall of which has now mostly fallen. Wall footings against the outer precinct walls indicate the locations of necessary buildings such as barns, stables, storehouses, bakehouses and brewhouses.
The western hall was extensively remodelled after 1500, perhaps by Bishop Sherbourne (1505-08), the thirteenth century windows were altered, the central window on the south was removed and replaced by a small chamber and the original timber ceiling of the undercroft was rebuilt as a line of masonry vaults. Stone gables were added to support the roof and an upper floor was also added to the hall. A surviving crenelated gatehouse to the inner courtyard was probably also built at this time. The last episcopal buildings added to the palace are from the early 16th century, perhaps at the time of Bishop Edward Vaughan (1509-22). There are footings of a large corn barn against the north boundary of the precinct dating from this time and a chapel which must have replaced and earlier one was attached to the north wall of the old hall, this has a fine late Perpendicular east window.
The monument is of national importance for its potential to enhance our knowledge of high status settlement organisation. It retains significant archaeological potential, with a strong probability of the presence of associated archaeological features and deposits. The structure itself may be expected to contain archaeological information concerning chronology and building techniques.
The scheduled area comprises the remains described and areas around them within which related evidence may be expected to survive.