The Castle the towers above Montgomery succeeded the motte-and-bailey castle at Hendomen about 1 mile to the north-west after 1233.
The situation for the site of the new castle was stronger, steep rocky outcrops made for a more defensive building that was military fashionable. The new castle was built during Henry III's campaign against Llywelyn ap Iorwerth in whose hands Hendomen had left but whose fidelity had been rendered questionable by his siege, early in 1233, of Builth Castle.
The new site consisted originally of an inner ward at the north end and constructed of stone between 1224 & 1233, the middle section to the south was built in wood then later converted to stone. The outer ditch to the south was added later. The current wooden bridge that crosses the rock cut ditch was the site of a drawbridge that connects to the middle section, a further bridge crosses another ditch and joins into the inner section of the castle.
The Crossing to the inner section of the castle was defended by a gatehouse with two rounded towers where much of the ground floor remains intact.
Each tower contained a rectangular room, not originally accessible from the gate passage, although a door was later installed into the tower on the west side, this may have originally been a prison.
The room on the east, where the drawbar across the gate would have been operated, is entered into the courtyard beyond where a number of mason marks scratched onto the stone, can be found. From models at the Old Bell Museum, a wooden chapel, supported on two posts, straddled the back entrance passage, both this and the three upper floors of the gatehouse were reached via stairs from the courtyard.
The two uppermost floors would have contained apartments.
The remaining inner defences consisted of a curtain wall with a tower on the north side and a large tower where the well is sited on the west.
This tower was built over the precipice along that side of the castle, this along with the seepage and well caused structural problems and had to be rebuilt in the 14th century.
The bakehouse, with two large bread-ovens and brewhouse can be found to the north-west and appear to be part of an early plan, but most of the entire section was filled with structures on several floors. The middle section shows traces of buildings which may have lined the inside sections, although it was later removed to make room for a fine half-timbered mansion with brick infilling built by Sir Edward Herbert around 1622.
The town below was not defended for some years after it's foundation in 1223.
The earthworks and palisade eventually built passed to the west of the castle and provided a further line of defence. The castle survived attacks from Llywelyn ap Iorwerth in 1228, and in 1231, when the town was burnt, and by Dafydd ap Llywelyn in 1245.
Llywelyn ap Gruffydd's work on Dolforwyn Castle four miles to the south-west, begun in 1273, helped to precipitate Edward I's successful 1277 campaign, after which the town walls were rebuilt in stone in 1279-80. Construction on the castle in 1283-8, after the final settlement of 1282, included a new hall, kitchen, chamber, bakehouse and granary.
Peace reduced Montgomery as a strategic position and by 1343 the castle started to fall into disrepair. It was refurbished by Roger Mortimer, second earl in 1359 and again by Henry VIII during 1530 ~ 1540. It last saw action under the Herbert’s during the civil war where it finally surrendered to the Parliamentarians in 1644. In 1649 it was demolished and with it the recently built mansion.