Today, the remains of Carmarthen Castle are tucked away between the council offices and retail shops. During its peak, however, the site would have dominated the medieval town which sprang up inside the remains of the Roman wall. Giraldus Cambrensis reported that the Roman wall was still surviving into the 12th century so it is likely that when William Marshal took control of the site, sometime in the late 12th century, he would have used these Roman fortifications to his advantage.
An earlier castle was thought to have been built further downstream but it is the medieval Norman castle remains, originally built in 1104 and strengthened by the Marshal, which would have formed the heart of the administrative centre of, not just the town, but the surrounding county.
The castle underwent a series of attacks and rebuilding episodes during the various campaigns between the Welsh and English in the 12th and 13th centuries. Among these episodes was the capture and destruction of the castle by Llewellyn the Great in 1215, after which extensive rebuilding work was undertaken by William Marshal the younger, earl of Pembroke, who had re-captured this and other west Wales castles in 1223. A licence was granted in that year to crenellate the castle which demonstrates that the occupant was in royal favour at this time.
Edmund Tudor, father of Henry VII died here in prision in 1456.
The site is currently owned and managed by Carmarthenshire County Council www.carmarthenshire.gov.uk.