England–Wales border point. In 926, Edward's successor Athelstan, "King of the English", summoned the Welsh kings including Hywel Dda of Deheubarth to a meeting at Hereford, and according to William of Malmesbury laid down the boundary between England and Wales, particularly the disputed southern stretch where he specified that the eastern bank of the Wye should form the boundary. By the mid-eleventh century, most of Wales had become united under the king of Gwynedd, Gruffudd ap Llywelyn. In 1055, he marched on Hereford and sacked the city. He also seized Morgannwg and the Kingdom of Gwent, together with substantial territories east of
River Wye river from Redbrook to Chepstow forms the border between England and Wales. The River Wye forms two Sites of Special Scientific Interest, one covering the Upper Wye ("Gwy Uchaf") above Hay-on-Wye, and one covering the Lower Wye ("Gwy Isaf") downstream to Chepstow. The criteria for inclusion of the river as an SSSI include geology, topography, flora, mammals, invertebrates, fish and birdlife, as the river and its tributaries constitute a large linear ecosystem. The Lower Wye SSSI is itself divided into seven units of assessment set by Natural England, and administrative responsibilities are shared between the county authorities of Powys, Herefordshire,