Grosmont Castle was one of a trio of earth-and-timber strongholds built by the Normans in the aftermath of the Conquest to guard the communication route between Hereford and Wales, together with Skenfrith Castle ) and White Castle). It lies within a wide moat (20m across), and a further second enclosure defined by scarps and ditches.
From the thirteenth century the site was re-built in the more durable local red sandstone, and timber defences were replaced by a stone curtain wall, protected by three circular towers and a gatehouse; a similar design to that of Cilgerran Castle. In the following century the buildings around the inner ward were remodelled to suit a noble household.
The castle was attacked and besieged by Gruffudd, son of Owain Glyndwr in 1405, before being relieved by a force from Hereford. By 1538 Grosmont was disused and abandoned. It came into state care in 1923.