Llansteffan is an impressive, dramatically sited stronghold crowning a hilltop overlooking the estuary of the River Tywi. Long before its construction an Iron Age hill fort of the 6th century B.C. occupied the site, its double ditch can still be seen on the west of the castle. The first Norman castle was created between the prehistoric defences: an earth bank surmounted by a timber palisade. This happened in the first years of the 12th century, but the castle was first mentioned in 1146 when it was captured by Lord Rhys and his brothers, princes of Deheubarth. The Norman recaptured Llansteffan after a first failed attempt, Rhys came again in 1189 but was unable to hold on to the castle.
In 1189 Llansteffan was in the hands of William the Camville and he started the transformation of the castle into a powerful stone fortress. The first step was the walling of the early Norman ring work but today only little part of this work survives on the north-west walls of the upper ward, the section facing the outer bailey was demolished. At the time the outer ward was encircled by timber defence. The De Camvilles refortified the stronghold and maintained control until 1338. During the intervening years Llywelyn the Great captured the castle when he conquered Deheubarth in 1215. William Marshal started the campaign of reconquest in 1223 and, after its victory, Geoffrey de Camville regained Llansteffan and strengthened the upper ward with the addition of the still-prominent square gatehouse (with two storeys above the gate passage) and a round mural tower (only its foundations are today visible).
Llansteffan was still far to acquire its present form, it happened only in the second half of the 13th century after another after another Welsh victory (The Battle of Coed Llathen – 1257) and a third recovery in Norman hands, William de Camville II started the reconstruction of Llansteffan, which was ended by his son Geoffrey. The timber defences of the lower ward were replaced with a stone curtain, reinforced by two U-shaped three- storeys towers (the West Tower, now ruinous, and the North Tower, today almost intact: this contained comfortable accommodation and at the junction with the curtain is endowed with two turrets, one housing latrines and the other the spiral stair) with a Great Gatehouse between them. Tthe vulnerable west side of the upper ward was heightened and strengthened to carry a wider wall-walk. The south front of the curtain, overlooking the crag, is tower-free but the south-east angle is projected outside to create a sort of bastion.
The masterpiece of Llansteffan was the twin towered Great Outer Gatehouse. It resembles the Inner East Gatehouse at Caerphilly  and predates the King Edward I’s Great Gatehouses of North Wales castles. Guard chambers flank the main entrance passage, which had murder holes in the vaults an portcullisat each end. In 1338 the last male heir of the de Camville family died and their estates passed into the female line, to Robert Penrees. By 1337 the Crown had regained control of Llansteffan Castle. but allowed the Penrees family to continue as custodians. In the early 15th Century the legendary folk hero Owain Glyndwr threatened English sovereignity and Sir John Penrees was ordered by the King to strenthen the castle. Nevertheless, Glyndwr’s men captured the fortress at Llansteffan for a short time, but it soon fell again back into the King’s hands.I n 1495 (by Jasper Tudor Earl of Pembroke, the only later Lord to occupy the castle) both ends of the passage have been walled up and a new entrance was built alongside to eliminate the inconvenience caused by portcullis winding gear in the above hall, that fully occupied the upper floor, and to provide extra accommodation. Two round stair turrets are at the inner corners of the keep-gatehouse.
Once the outer curtain was complete it become the more formidable defence of the castle and a portion of the inner curtain facing the outer bailey was demolished to create a single large enclosure. In the 15th century a large barn was erected between the north tower and the bastion. When the military importance of the site declined Llansteffan passed into obscurity and after a long period of neglect in 1959 the castle was placed in State care and is now maintained by CADW. Free admission.