Grosmont Castle was one of a trio of earth-and-timber strongholds built by the Normans in the aftermath of the Conquest to guard the communication route between Hereford and Wales, together with Skenfrith Castle (NPRN 93431) and White Castle (NPRN 94853). It lies within a wide moat (20m across), and a further second enclosure defined by scarps and ditches. From the thirteenth century the site was re-built in the more durable local red sandstone, and timber defences were replaced by a stone curtain wall, protected by three circular towers and a gatehouse; a similar design to that of Cilgerran Castle (NPRN 95037). In the following century the buildings around the inner ward were remodelled to suit a noble household. The castle was attacked and besieged by Gruffudd, son of Owain Glyndwr in 1405, before being relieved by a force from Hereford. By 1538 Grosmont was disused and abandoned. It came into state care in 1923. (Cofleinref. Knight, 2000)
First castle on site in existence by 1154, which consisted of wooden buildings defended by a palisade and ditch, but only the moat remains of this earliest period. The masonry castle was built in 3 main periods. The Great Hall is the earliest structure, dating from about 1210. The second building period, during the first half of the C13th, saw the enclosure of the inner ward, with a stone curtain flanked by 3 semi-circular towers and a projecting gatehouse. The final stage, probably around 1330, included the addition of a range of rooms outside the N curtain and the enlargement and heightening of the SW tower.
The stone castle stands on a roughly rectangluar platform surrounded by a ditch 6m deep. The remains of a probable bailey encircling the castle can be traced on the SE and NE as a scarped slope 4m high, and on the N as 2 banks 0.3m high and 9m wide with an intermediate ditch 1m deep. (Glamorgan-Gwent Archaeological Trust HER)
On a flat elevated plateau, some 100m NW of Grosmont village, approached along a narrow lane from the main street.
Following the initial conquest of the Welsh kingdom of Gwent by William Fitz Osbern, Lord of Breteuil in Calvados, between 1067-75, the Normans built a triangle of castles - Grosmont, Skenfrith and White Castle - to control their newly won lands. These late C11 defences would have been of earth and timber. At Grosmont the great ditch of that ringwork castle still survives, the perimeter of which would originally have been protected by a wooden palisade and timber gate tower. In July 1201, King John granted the three castles to Hubert de Burgh, who completely rebuilt Grosmont in stone, beginning with the rectangular hall-block (1201-4). Work stopped in 1205 after Hubert was captured whilst fighting for King John in France. Whilst he was still prisoner John granted the three castles to William de Braose of Abergavenny, in royal favour at the time. A prolonged dispute over the ownership of the castles then ensued, but in December 1218 this was settled by the King's Court in Hubert's favour. Hubert regained possession of Grosmont and between c1219-1232 embarked upon a major rebuilding programme, replacing the timber defences by a stone curtain wall with round towers at the angles, in the defensive style of the early C13. During the C14, the Earls of Lancaster carried out various alterations to Grosmont. The buildings around the inner ward were remodelled c1330 (either by Henry of Lancaster or his son, Henry of Grosmont) and alterations were made to the northern chamber block, including the addition of an elegant octagonal chimney shaft, and to the gatehouse which was extended to incorporate a drawbridge. The last fighting at Grosmont took place during the war of Owain Glyndwr, who attacked Gwent during the summer of 1404, but was defeated at the battle of Campston Hill. In 1825 the Duchy of Lancaster sold the ruins to the Duke of Beaufort and in 1923 they were given to the state by Mrs Frances Lucas-Scudamore.
C20 wooden bridge gives access to inner ward of castle, the surviving ruins are built of local red sandstone rubble and ashlar, and form the complete ground-plan of the castle with hall block to east and curtain wall to west. Much of SW tower of the curtain wall stands, but few remains of gatehouse survive. Hall Block, originally two-storeys with upper hall. Raking plinth, west corners have ashlar quoins. Ground-floor has tall, narrow lancets: four in each of the long walls, one in the NW wall and two on SE side. The interior shows that the taller, corresponding lancets at first-floor level were originally set in wide segmental headed openings. Two of these survive, either side of the hall fireplace at S end. Below, a stone spiral stair (formerly linking ground-floor with upper hall) is set in an embrasure in left corner. In centre of hall block are remains of a stone partition wall, probably dating from the remodelling of c1219. SW Tower once formed one of three round towers of the C13 curtain wall, but in C14 the rear facade was rebuilt and enlarged. This courtyard front is buttressed with a tall pointed entrance arch on ground floor and, above, a single opening at first and second floor levels. Interior has deep circular basement, ground-floor chamber has three archers loops in splayed embrasures with two-centred arched heads. Access to upper floors, largely rebuilt in C14, is by spiral stair to right of entrance arch. First floor has three windows in arched recesses facing west. Each of the floors has a fireplace on the NW wall, including upper floor fireplace with chamfered jambs. Northern Block was built on site of third tower of C13 curtain wall, demolished when C14 block was built. The most notable surviving feature of this building is the elegant octagonal chimney with slender shaft rising from a raked and moulded base to delicately worked trefoil headed gablets on each face and a coronet-like top above. (Listed Building Report)
The early hall at Grosmont was most probably built within forty years either side of 1110. It still stands two stories high and has many features of comfort within its walls. There are many reasons to believe that this hall was built early in the castles history for the evidence points clearly to Grosmont castle having been fortified in stone from the first. Who actually first built the castle though, is more of a problem. Both the first earls of Hereford and Pain Fitz John had a great deal of wealth and ruled Gwent at a time when the stable rule of the Normans in Wales seemed inevitable. Grosmont hall is certainly not a fortress. It was built as the administrative centre of a barony with both comfort and administration in mind. White Castle to the west, however, was built as a fortress from the first, probably in concert with the foundation of Grosmont. Orcop to the east, a true motte and bailey castle, may be older. (Remfry)