Around 1102 Robert Fitzhamon, the first Norman Lord of Glamorgan bequeathed the lands of Llanblethian as a lordship to Herbert de St Quentin who is thought to have built the first fortification at the site of the castle.

This initial construct was believed to have been a simple ringwork defence with timber walls, a bank and ditch.

This was thought to have been roughly after 1307, but Gilbert de Clare was killed in the Battle of Bannockburn in 1314 before the castle was completed.

Modern historians believe that the lack of inner courtyard buildings and the weakness of the curtain wall points to the hypothesis that the castle was never fully completed.

The ivy-clad gatehouse is between these and is a substantial structure where you can see the slits for the two portcullises and the fittings for the sets of strong doors.