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Monmouth Castle now exists as a ruin, tucked away behind the town’s main shopping street. Strategically located at crossings of the River Wye and River Monnow, there are now only a few fragments segments of ruin dating from the 12th-century Great Tower and 13th-century hall, a sad indictment of this once-important castle.

Founded in the 11th century by a Norman lord known as William Fitz Osbern, by the mid-14th century Monmouth Castle was in the hands of Henry of Grosmont, who altered the tower with much larger decorated windows, making it less practical for defending, whose outline can still be seen in the east wall.

The most notable event in the tower’s history arguably occurred on 16 September 1387, when King Henry V, hero of the Battle of Agincourt was born here, an occasion commemorated at Monmouth’s Agincourt Square. As a king he is immortalized in one of Shakespeare’s last plays from the 16th century, and famously depicted by Kenneth Branagh in the 1989 film adaptation.

The original timber fortress was amplified with stone defences some time during the period in the 12th century known as the Anarchy (a brief civil war between supporters of King Stephen and Queen Maud).

Over the course of its history, the castle was captured briefly by Simon de Montfort during the Baron’s War, but eventually passed to Edmund Crouchback, Henry III’s second son and the 1st Earl of Lancaster. It was during this period that Crouchback added the castle’s Hall and strengthened the defences further. As the castle grew, so did the town that was developing around it.

Only fragments of this once important castle now remain. The curtain wall, gatehouse and great round keep, the iconic parts of the castle designed for protection, which stood until the Civil War where the Great House now stands, have now completely vanished.

A small section of the town’s museum records the early defences of Monmouth and its castle. The site is now home to a recreated medieval courtyard garden with herbs, named the ‘King’s Garden’. The castle remains are roughly oval, about 140 metres long and 90 metres wide, with steep cliffs to one side.

All that is left is the ruined Great Tower and Hall. These stand on the edge of a slope heading down to the river Monnow, on the west side of the formerly great castle. Still partly apparent is a ditch in gardens behind Agincourt Square. Half-way along Castle Hill Road was the former entrance to the castle, consisting of a bridge and strong gatehouse, although these too are no longer in existence.

The castle’s end came during the English Civil War, when it changed hands three times and was eventually slighted by Parliamentary troops. A local diary for 1647 states that on 30th March some local townsmen and soldiers began pulling down the iconic great round tower, which stood where Great Castle House now stands, and that on 22nd  December at ‘about 12 o’clock, the Tower in the castle of Monmouth fell down, upon its side, whilst we were at sermon’. The Great Castle House was built in 1673 by Henry Somerset, later the duke of Beaufort, was to replace his family’s residence in the country following the Civil War. In 1875 the house became the headquarters of the Royal Monmouthshire Royal Engineers (Militia), and as such it remains one of the few British castles still under military occupation.