The Battle of Monmouth took place in 1233, probably on 25 November of that year, although some sources suggest 26 December. The fighting was between those loyal to Henry III, King of England, and the forces of Richard Marshal, Earl of Pembroke and Lord Marshal of England, who had formed an alliance with the Welsh prince Llywelyn ap Iorwerth and his supporter Owain ap Gruffudd, a grandson of Rhys of Deheubarth.
Richard Marshal was a leader of the barons opposed to the growth of King Henry's powers, and an adversary of the king's foreign allies at court, notably the Poitevins Peter de Rivaux and Peter des Roches. Marshal refused to attend Henry's court at Gloucester in August 1233, and Henry declared him a traitor. Marshal retired to his castle at Striguil (Chepstow), while the king and his army moved west to Abergavenny. In response, Marshal joined with Owain to seize the castles at Cardiff and Newport before attacking Abergavenny, Grosmont and Monmouth. In the pitched battle for Monmouth, Marshal's troops defeated those led by the local lord, John of Monmouth (c.1190-1248), and slaughtered the supporters of the king, who had already retreated to Gloucester.[1][2][3]
The Glamorgan-Gwent Archaeological Trust refer to the battle as having taken place at Castle Field, to the west of the River Monnow,[3] land today known as Vauxhall Fields. Other sources suggest that the Monnow Bridge and the Church of St Thomas the Martyr, located to the south-west of the town, were damaged by fire in the fighting.[4]
After the battle, John of Monmouth seems to have returned to take control of the town. Marshal travelled to Ireland to rally his supporters there. He agreed a truce with Henry early in 1234, but died of wounds sustained in the Battle of the Curragh shortly afterwards.[1]