By the time the Civil War broke out in 1642, Denbigh Castle had been slowly decaying for generations. Colonel William Salesbury, a fiercely loyal Royalist known locally as 'Old Blue Stockings', had the castle repaired and refortified, and it became a stronghold for the king's cause in North Wales.
In April 1646, with the Royalist cause collapsing elsewhere, a Parliamentary army under Sir Thomas Mytton laid siege to Denbigh. Salesbury's garrison of around 500 men held out for six months, with some of the fiercest fighting centred on the Goblin Tower on the town walls — the polygonal tower that protected the castle's water supply, and which still bears the scars of Mytton's siege guns.
Salesbury refused to surrender even as the wider Royalist war effort disintegrated, and only laid down arms on 26 October 1646 after King Charles I personally ordered him to do so. Denbigh has the distinction of being the last major mainland fortress in Britain to fall in the war. In the aftermath, Parliament ordered the castle to be slighted — deliberately damaged to prevent further military use — and it was allowed to fall into the picturesque ruin visitors see today.
By 1646, Denbigh Castle was one of the last significant Royalist strongholds left standing in North Wales as the first English Civil War drew to its close. Colonel William Salusbury, known as 'Old Blue Stockings', commanded the garrison and held out through a six-month siege by Parliamentarian forces under General Thomas Mytton, refusing to surrender even as the wider Royalist cause collapsed around him.
Salusbury finally yielded the castle in October 1646, but only after receiving a direct order to do so from King Charles I himself, a mark of the loyalty and tenacity of the defence. In the aftermath, Parliament ordered the castle to be slighted — deliberately damaged to prevent its future military use — which explains much of the ruined state in which the castle survives today.