| Grosmont Castle | |
|---|---|
| Grosmont, Monmouthshire, Wales | |
 Grosmont Castle, seen from the north-west | |
  Grosmont Castle | |
| Coordinates | 51°54′55″N 2°51′57″W / 51.915278°N 2.865833°W |
| Type | Castle |
| Site information | |
| Controlled by | Cadw |
| Open to the public | Yes |
| Condition | Ruined |
| Site history | |
| Materials | Old Red Sandstone |
| Events | Norman invasion of Wales Glyndŵr Rising |
Listed Building – Grade I | |
| Reference no. | 1949 |
| Reference no. | MM007 |
Grosmont Castle is a ruined castle in the village of Grosmont, Monmouthshire, Wales. The fortification was established by the Normans in the wake of the invasion of England in 1066, to protect the route from Wales to Hereford. Possibly commissioned by William fitz Osbern, the Earl of Hereford, it was originally an earthwork design with timber defences. In 1135, a major Welsh revolt took place, and in response King Stephen brought together Grosmont Castle and its sister fortifications of Skenfrith and White Castle to form a lordship known as the "Three Castles", which continued to play a role in defending the region from Welsh attack for several centuries.
King John gave the castle to a powerful royal official, Hubert de Burgh, in 1201. During the course of the next few decades it passed back and forth between several owners, including Hubert, the rival de Braose family, and the Crown. Hubert rebuilt the castle in stone, beginning with a new hall and then, on regaining the property in 1219, adding a curtain wall, gatehouse and mural towers. In 1233, a royal army camped outside the castle was attacked by rebel forces under the command of Richard Marshal. Edmund, the Earl of Lancaster, gained possession of the castle in 1267, and it remained in the hands of the earldom and later Duchy of Lancaster until 1825.
Edward I's conquest of Wales in 1282 removed much of Grosmont Castle's military utility, although it was besieged in 1405 during the Glyndŵr Rising. By the 16th century it had fallen into disuse and ruin. The castle was placed into the care of the state in 1922, and is now managed by the Cadw Welsh heritage agency.