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
Wales vessels lost and an average loss of life of about 78 sailors per year. Wartime action caused losses near Holyhead, Milford Haven and Swansea. Because of offshore rocks and unlit islands, Anglesey and Pembrokeshire are still notorious for shipwrecks, most notably the "Sea Empress" oil spill in 1996. The first border between Wales and England was zonal, apart from around the River Wye, which was the first accepted boundary. Offa's Dyke was supposed to form an early distinct line but this was thwarted by Gruffudd ap Llewellyn, who reclaimed swathes of land beyond the dyke. The Act of Union of