Although the ruins are substantial, and have a spectacular setting on a narrow, rocky spur, Montgomery Castle seems to be a relatively little visited site, perhaps due to its rather out-of-the-way location, in hilly land near the England-Wales border. The castle overlooks the small town of Montgomery, the ancient county seat of Montgomeryshire; both were established around the start of the 13th century, a few miles west of Offas's Dyke, which defined the traditional boundary between the two countries. The fortification was involved in the wars of the Welsh Marches, until the 1290s, but saw very little further action; it was not destroyed, but remained occupied (later used, amongst other purposes, as a prison), and eventually part was converted into a country mansion. However, both this and the remaining parts of the castle were slighted by order of Parliament in 1649, during the later stages of the Civil War, and subsequently much of the masonry was removed for use elsewhere.
The remains comprise the curtain walls of the two main protected areas, the inner and middle wards, separated by deep, rock-cut ditches, plus part of the gatehouse including a tall wall from its western tower, and a similarly large section from another tower, also on the west side. The castle certainly looks very dramatic, especially from below, as here the dark grey walls can be seen rising high above the similarly coloured volcanic conglomerate bedrock. Views from the top are extensive, and the site as a whole is one of the best ancient monuments in the county. The castle is free to enter, and approached from a short path to the south; parking is available close by, along a steep road up from the town centre.
The first castle near Montgomery was a timber structure, built by Roger de Montgomery in 1070, on top of a hill overlooking an important ford on the River Severn, at Rhydwhyman half a mile west, and was later occupied by the de Boulers family. The site is now known as Hen Domen and while the castle motte can still be seen, there are no other visible structures and the land is privately owned. Nevertheless this castle was relatively substantial for its time, containing various wooden buildings, and was inhabited for over a century, until mostly destroyed in 1215 during a Welsh insurgency, after which the decision was taken to rebuild in stone half a mile east, on a slightly lower though better defensible spur. The reconstruction was supervised by Hubert de Burgh, 1st Earl of Kent (died 1243), who was also responsible for the Three Castles of Monmouthshire (Skenfrith, Grosmont and White). The first phase of this new fortress was complete by 1228, when the chief components were the gatehouse, set between two D-shaped towers, a larger tower to the west, a curtain wall all around a courtyard, rising to the same height as the towers, and several lesser rooms on the inside. Access was via a bridge over a vertical-walled rock ditch at the front (south). A second fortified area, the middle bailey, was added a few years later, also entered via a bridge across a rock channel, while south of this was a smaller enclosure, the barbican. From the start of the 14th century there was a gradual change in use, from military to residential, culminating in an elegant, timber and brick house being raised in the middle ward, complete in 1625, for Sir Edward Herbert, though this endured for little more than 20 years, up until the deliberate destruction during the Civil War. Prior to this, the only other significant event was the 1402 siege of Montgomery instigated by the Welsh rebel Owain Glyndwr, during which the town was destroyed though the castle survived intact.
The ruins of Montgomery Castle can be seen from many places in town, on the crest of a wooded slope to the west; approach is along a steep road, leading to the small parking area, in front of Old Castle Farm. A path heads north, around a corner and out to an open area on the south side, side of the barbican, the outermost fortified area, now merely an earthen mound though originally enclosed by masonry walls. To the north, on the far side of a rock ditch originally 20 feet deep, is the larger, rectangular middle ward, lined by low stone walls dating from around 1253 (replacing an earlier timber enclosure), plus foundations of two round towers, either side of the south gatehouse. Other, lower walls on the inside are from the 17th-century mansion. A bridge over a second, wider ditch takes visitors to the inner ward, the oldest part of the castle. At the entrance are the remains of the inner gatehouse, a straight passage, once protected with two pairs of doors and a portcullis, between the lower portion of the two flanking towers, adjoining ground floor rooms. About here were other rooms, on three more floors, including the main residential suite, and a chapel. The tallest sections of the ruin are the west wall of the west gatehouse tower, and the north wall of the main west tower; this contained the castle well, sunk to a depth of 200 feet. Curtain walls surround the rest of the inner ward, still quite high to the west, but lower on the other sides. Within here are the remains of other internal walls, most dating from later modifications, as in its later stages the inner courtyard was lined with a row of timber buildings resting on masonry foundations.