River Wye given a Latin name "Vaga", an adjective meaning 'wandering'. The Tithe map references a Vagas Field in both Whitchurch and Chepstow. Philologists such as Edward Lye and Joseph Bosworth in the 18th and early 19th centuries suggested an Old English derivation from "wæg", "wave". The source of the Wye is in the Welsh mountains at Plynlimon. It flows through or past several towns and villages including Rhayader, Builth Wells, Hay-on-Wye, Hereford (the only city on the River Wye), Ross-on-Wye, Symonds Yat, Monmouth and Tintern, meeting the Severn estuary just below Chepstow. Its total length is . The lower of the
England–Wales border its residents at the time spoke Welsh. In the late 17th century under Charles II it was added to the Oxford circuit of the English Assizes, following which, according to the 1911 Encyclopædia Britannica, it gradually "came to be regarded as an English county". Under that interpretation, the boundary between England and Wales passed down the Rhymney valley, along Monmouthshire's western borders with Brecknockshire and Glamorgan, so including Newport, and other industrialised parts of what would now generally be considered to be South Wales, within England. The 1911 Encyclopædia Britannica unambiguously described the county as part of England, but noted