Chepstow Castle (Welsh: Cas-gwent), located in Chepstow, Monmouthshire in Wales, on top of cliffs overlooking the River Wye, is the oldest surviving stone fortification in Britain. It was built under the instruction of the Norman Lord William fitzOsbern, soon made Earl of Hereford, from 1067, and was the southernmost of a chain of castles built along the English-Welsh border in the Welsh Marches.