Monmouthshire was the most border of all counties, straddling England and Wales throughout its 400 years' history. It was bisected by the Usk, the Monnow, from which its name derived, forming the northern boundary, the Wye its eastern, and the Rhymney the western. The coastal plain and gentle hills of the south-east gave way to rugged mountains and valleys in the north-west.

In pre-Roman times, the area was part of the territory of the Silures. It was rapidly brought under Roman control, the remains at Caerleon and Caerwent being among the most impressive in the country. It stayed British after the Romans left, for some time formed an independent kingdom of Gwent, and at others was part of the kingdom of Deheubarth.

The Normans began systematic colonization after 1066, constructing castles at Chepstow, Raglan, Usk, Monmouth, White Castle, Skenfrith, Grosmont, and Abergavenny, as well as protected boroughs like Newport. The region was divided up into marcher lordships, which defended it as best they could from Welsh attacks: even so, Grosmont, Abergavenny, and Newport were burned in Glyndŵr's rebellion in the early 15th cent. The remote region was known mainly for the excellence of its archers and for the woollen Monmouth caps which were popular. Henry V was born in Monmouth, where his statue adorns the town hall. The advent of the Tudors, a Welsh dynasty, changed the status of the area. By the Act of Union of 1536, the territory was incorporated into England, joining with land to the west of the Usk to form the new county of Monmouthshire. Its peculiar position was reflected by the fact that, like English counties, it was given two knights of the shire, but Monmouth had only one member and shared the representation with six contributory boroughs on the Welsh pattern. The most enduring interests were those of the Herberts, earls of Pembroke, who eventually concentrated on their Wiltshire properties; the Somersets, earls of Worcester and future dukes of Beaufort, who owned Troy House and Raglan castle; and the Morgans of Tredegar. The Somerset family dominated the borough of Monmouth, while the county was usually shared. The Somerset interest was powerful enough to secure the county for the king during the Civil War, though it was harassed by parliamentary forays from Gloucester. Charles I stayed at Raglan late in the war and it was the last royalist stronghold to surrender, in August 1646, when the garrison marched out with full honours. Along with Monmouth and Abergavenny castles, Raglan was then slighted.

The western parts of the county were little developed, though Camden noted in 1586 that they were ‘not unserviceable to the industrious husbandman’. The large-scale exploitation of the coal and iron resources of Monmouthshire began in the early 19th cent., transforming the economic and political balance. Monmouth, the largest town in 1801 with 3,300 inhabitants, was by 1871 outstripped by Abergavenny, Pontypool, Blaenavon, Tredegar, and Newport. The last had grown from about 1,400 persons in 1801 to 40,000 by 1871 and more than 100,000 by 1961. Politically the county became first a Liberal, then a Labour stronghold. In 1831 Samuel Lewis wrote that there were churches in the shire where the services were in English, others in Welsh, and still others where the language alternated: ‘the antipathy of the people to the introduction of the language and manners of the English is still inveterately strong … they stigmatise every thing assimilating to what is English with the epithet of Saxon.’ By the mid-20th cent. the Welsh language had retreated and the opening of the Severn bridge in 1966, replacing the old Beachley–Aust ferry, suggested that Monmouth was being pulled back into the English economic orbit. The Local Government Act of 1972 moved the county back into Wales, restoring the name of Gwent, and Monmouth, which had always been on the eastern extremity of the county, lost its position to Cwmbran, a new town just north of Newport. Even this was not the last throw, for in 1996 a further reorganization of local government divided Gwent into four unitary authorities, one of which was to be called Monmouthshire. A better example of the importance which people attach to names could scarcely be found.

J. A. Cannon