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.
Edward I’s conquest of Wales in 1282 removed much of Grosmont Castle’s military utility, although it was besieged in 1405 during the Glynd?r 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.