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
River Monnow Kentchurch weir for the first time for many years in the Autumn of 2008. The Monnow Rivers Association takes a large amount of the credit for the improvement in the fishing through their work on habitat improvement throughout the catchment and encouraging anglers to return a high proportion of fish caught safely to the water. River Monnow The River Monnow () marks the England–Wales border for much of its length. After flowing through southwest Herefordshire, England, and eastern Monmouthshire, Wales, its confluence with the River Wye is approximately south of Monmouth. The Monnow rises near Craswall on Cefn Hill just