A Norman castle town on the Welsh March where the Monnow meets the Wye, held by the house of Lancaster from 1267, birthplace of Henry V in 1386, namesake of Geoffrey of Monmouth, and home of Britain's only river bridge whose medieval gate still stands on the bridge.
Monmouth stands on a low spur where the River Monnow flows into the Wye, a few kilometres west of the modern border between Wales and England. The Normans built a castle there within a few years of 1066, and a borough, a Benedictine priory and a fortified bridge grew up around it. For almost five centuries it was the head of a lordship of the Welsh March, governed by its lord rather than by the sheriff of an English county or by a Welsh prince, until the Laws in Wales Act of 1536 made it the county town of the new shire of Monmouthshire.
From 1267 the castle belonged to the earls and dukes of Lancaster, and in 1386 Mary de Bohun gave birth there to the future Henry V of England, long remembered as Henry of Monmouth. The town also gave its name to Geoffrey of Monmouth, whose History of the Kings of Britain carried King Arthur into European literature, and it keeps the only river bridge in Britain whose medieval gate tower still stands on the bridge itself.
The Romans placed a small fort, Blestium, at the crossing on the road between Gloucester and Caerleon, and in the later Roman period the site was a centre of ironworking using local ore and charcoal. After Roman rule the area lay at the southern edge of the Welsh kingdom of Ergyng, and a church of St Cadoc is recorded there in the seventh century at an unknown spot. The Welsh name was first Abermynwy, the mouth of the Monnow, and later Trefynwy, the town on the Monnow.
William FitzOsbern, whom William the Conqueror made earl of Hereford to hold the border, built the first castle before his death in 1071, on the rise above the Monnow as a partner to his larger fortress downstream at Chepstow. It began as an earth and timber ringwork and was rebuilt in stone before about 1150. When FitzOsbern's son Roger rebelled and forfeited his lands in 1075, Monmouth went to a Breton lord, Wihenoc, who founded a priory beside the castle as a dependency of the abbey of Saint-Florent at Saumur; its church was consecrated in 1101. Domesday Book counted Monmouth under Herefordshire in 1086, but Wihenoc's successors of the Monmouth family ruled it as a lordship of the March.
The March was a patchwork of lordships carved out of Welsh territory, where the lord exercised rights that in England belonged to the king: he held his own courts, built castles and made war without licence, and no royal sheriff entered his land. Monmouth was one of these lordships, although its parish lay in the English diocese of Hereford rather than the Welsh see of Llandaff, as it did until 1836. The borough lived by its market along Monnow Street and by ironworking: charters mention forges fed with local ore, and their cinder heaps gave Cinderhill Street in Overmonnow its name. That suburb across the Monnow was protected by its own defensive ditch, the Clawdd Du, by the twelfth century.
The March's loyalties were tested in 1233, when Richard Marshal, earl of Pembroke, rebelled against Henry III of England. On 25 November Marshal rode to reconnoitre Monmouth, which the king had entrusted to the Flemish lord Baldwin of Guînes with a garrison of Flemings and Poitevins, while the lord of Monmouth, John of Monmouth, was away. According to Roger of Wendover, Baldwin sallied out believing Marshal had few men with him and was routed when the earl's force came up, and a drawing in the St Albans chronicle shows Marshal unhorsing Baldwin. The castle held out, and Wendover's account may mean that the timber bridge over the Monnow and the church of St Thomas in Overmonnow were burned in the fighting.
After the death of John of Monmouth in 1248 the lordship came into royal hands. Following a brief seizure by Simon de Montfort, Henry III granted it in 1267 to his younger son Edmund Crouchback, earl of Lancaster, together with the Three Castles of Grosmont, Skenfrith and White Castle to the north-west. Edmund made Monmouth his main residence in the region and rebuilt its hall, and in the early fourteenth century, probably under his grandson Henry of Grosmont, later duke of Lancaster, the Great Tower was given a new roof and tall traceried windows in its upper floor.
The castle had a part in the fall of Edward II of England. Captured in Glamorgan in November 1326, the king was brought to Monmouth, and on 20 November, at the demand of Queen Isabella and their son, he surrendered the Great Seal there before being taken on to Kenilworth. In 1361 the Lancastrian inheritance, Monmouth included, passed through Blanche of Lancaster to her husband John of Gaunt, and from them to their son Henry Bolingbroke, whose household used the castle on its travels between the Lancastrian estates.
Bolingbroke's eldest son was born at Monmouth Castle, by local tradition in a chamber above the gatehouse, to his wife Mary de Bohun, then sixteen or seventeen. Because a son of Richard II's cousin stood far from the throne, the birth was not formally recorded, and both 1386 and 1387 were long argued for; modern scholarship favours 16 September 1386. The boy was known as Henry of Monmouth until his father took the crown in 1399 and created him Prince of Wales.
The prince learned war in the rising of Owain Glyndŵr, which came close to the lordship. According to the Annals of Owain Glyndŵr, an English force was beaten in 1404 at Craig-y-dorth, about a mile south-west of Monmouth, and chased to the gates of the town. Glyndŵr's followers burned Grosmont and Abergavenny, but Monmouth and its castle were never attacked, and in March 1405 troops of the prince's household defeated a Welsh force at Grosmont, a victory Henry announced to his father by letter. Ten years later, as king, he won the Battle of Agincourt.
Monmouth made much of the connection. In Shakespeare's Henry V the Welsh captain Fluellen compares Monmouth with Macedon, birthplace of Alexander the Great, because each has a river with salmon in it. In 1792 the townspeople set a statue of the king on the front of the Shire Hall, whose market square, later renamed after his victory, occupies the former outer bailey of the castle.
The town's other famous name belongs to a writer known almost only through his books. Geoffrey called himself Galfridus Monemutensis, and contemporaries also knew him as Geoffrey Arthur. He was born around 1095 to 1100, possibly into one of the Breton families settled in the lordship since Wihenoc's time, because both his names were commoner among Bretons than among the Welsh. He may have had links with the priory, but his adult career lay at Oxford, where he witnessed charters between 1129 and 1151, probably as a canon of the collegiate church of St George, and in 1152 he was consecrated bishop of St Asaph, a see he probably never saw. He died around 1155.
His History of the Kings of Britain, finished around 1136 to 1138, traced British kings from Brutus of Troy to the seventh century and gave Arthur, Merlin, Leir and Cymbeline the forms later writers used. Geoffrey claimed to be translating an ancient British book lent to him by Walter, archdeacon of Oxford. William of Newburgh wrote around 1190 that everything Geoffrey said about Arthur was invented, but the book survives in more than 200 manuscripts and was turned into Norman French verse by Wace and into Welsh prose as Brut y Brenhinedd. In Monmouth the ornate oriel called Geoffrey's Window, in the former priory buildings, was built in the mid-fifteenth century, three centuries after his death, and probably belonged to the priory gatehouse.