Grosmont Castle is one of three in Monmouthshire which for a time were held together for a period to form a single lordship. The other castles were Skenfrith and White Castle. Visiting the three together makes for a fascinating day of immersion in the history of the Marches.

The early structure at Grosmont, constructed soon after the Norman conquest, would have been a motte surrounded by a moat protecting a timber castle and palisade.

During an extensive programme of building, carried out between 1219 and 1232, the stone fortress was built, but some aspects of the stone castle may predate this.

Certain austere military features were softened somewhat in the 14th century when wider windows replaced arrow slits and fireplaces and garderobes were added. Two buildings were added outside the curtain wall of the castle, one of which boasts the ashlar chimney pot which is considered an exceptional survival of the medieval period.