Einion o'r Porth and Rhys ap Gruffydd of Deheubarth entertained Baldwin of Exeter, Archbishop of Canterbury and Giraldus Cambrensis here in 1188 during their famous tour of Wales recruiting for The Crusades.

As a result, the previous overlord Rhys ap Gruffydd returned and sacked the castle before winning the battle of Radnor against Roger Mortimer and Hugh de Say.

After the death of the last Braose of Radnor the castle was taken into royal or crown custody but was destroyed by Prince Llywelyn ab Iorwerth in 1231.

In 1264 Prince Llywelyn ap Gruffudd allied with Simon de Montfort, 6th Earl of Leicester took and again destroyed the castle.

Owain's forces allegedly attacked it in either 1401 or 1403, capturing the garrison of sixty men inside, whom he then hanged from the curtain walls over the battlements, then beheaded and buried nearby.

By 1405 King Henry IV of England had regained the castle and garrisoned it with a new force of thirty men-at-arms and one hundred and fifty archers under the command of Richard, Lord Grey.

Radnor castle then gently fell into decay in the more peaceful times and by 1538 only one tower remained habitable and that was used as the county prison.

During the English Civil War the castle was visited by King Charles I in 1642 but after a siege was captured and dismantled by Parliamentary forces to prevent it becoming a Royalist stronghold again, a process known as slighting.

The rest of the stonework must have been used as a ready supply of cut stone and was depleted by the local people for their homes and farms and some became buried, emerging in digging in the 19th century.

The earthworks consist of a large mound or motte, protected to the north by a double ditch, probably built by the earl of Cornwall in 1233.

One man involved, later Sir Robert Harley, 1st Earl of Oxford and Mortimer, becoming MP, three times Speaker of the House of Commons and also Chancellor of the Exchequer in 1710 and later Lord High Treasurer, and very nearly Prime Minister.

The monument was built in memory of Sir George Cornewall Lewis (1806–1863) and designed in High Victorian Gothic style by John Gibbs.

New Radnor's main sources of income and jobs and employment opportunities are still from farming and agriculture and today there are new smaller businesses such as cider making, picture framing and holiday homes, bed & breakfast establishments and tourism in general.

Other than the small station 1⁄2 mile (0.80 km) from the town, the plans never came to fruition, only allowing services on the Great Western Railway to both Leominster and onwards to London Paddington.