The Norman invaders built St Clears Castle in about 1100. By the middle of the 12th century, it had become the centre of a Norman lordship despite the fact that it was besieged, burnt and captured by the Welsh princes in 1153, 1189 and 1215. It was surrendered to Owain Glyndŵr in 1405 but was abandoned shortly afterwards.
In 1188, 12 archers from the castle murdered a young Welsh noble and were ordered to go on the crusade as punishment.
St Clears Castle is a motte and bailey. Shown in the picture on the interpretative panel is the immense motte or mound, which rises to 12m – one of the tallest in Wales.
At first, it would have carried a timber tower but foundations seen in the past suggest that a stone-keep was built later.
The courtyard or bailey has been levelled and is unexcavated. However old photographs show that the defensive banks that may have carried stone walls (possibly built by William Marshal the Younger when he received the castle in 1230), and also the outline of buildings within the bailey. These would have included a Great Hall, where the entire garrison ate, drank and slept, the kitchens, a chapel, stables and workshop.