England–Wales border after Harold's death at the Battle of Hastings, Wales was again divided without a leader to resist the Normans. Immediately after the Norman conquest of England, King William installed one of his most trusted confidants, William FitzOsbern, as Earl of Hereford. By 1071 he had started the building of Chepstow Castle, the first castle in Britain built of stone, near the mouth of the Wye. It served as a base from which the Normans continued to expand westward into south Wales, establishing a castle at Caerleon and extinguishing the Welsh kingdom of Gwent. William also installed Roger de Montgomerie at
Wye Valley well as in the adjoining Forest of Dean. The medieval boroughs of Goodrich and Chepstow, at each end of the Wye Gorge, may have originally been established at this time. Closely following the River Wye, Offa's Dyke was built in the 8th century under King Offa to mark out the boundary between England and Wales and is, today, the longest archaeological monument in Britain. Offa's Dyke Path long distance footpath today traces the route through the Wye valley on the English bank, while the Wye Valley Walk follows the Welsh bank. When the Normans conquered the region in the 11th