Tenby Castle Tenby Castle is a fortification which stands on a headland separated by an isthmus from the town of Tenby , Pembrokeshire , Wales . The remaining stone structure date from the 13th century but there are mentions of the castle from as early as 1153 . St Catherine ' s Fort , a Palmerston Fort , stands just offshore of the medieval castle . History . The castle , which was sited on a rocky promontory , was founded by the Normans during their invasion of West Wales in the 12th century . A stone tower was built on the headland ' s highest point which was protected by a curtain wall . The walls had a gateway and several small towers on the landward side . A lesser sea wall surrounded the remainder of the site and the beach area to the west . In 1153 , the castle was captured and destroyed by Maredudd ap Gruffydd and Rhys ap Gruffydd , the future ruler of the south - western petty kingdom of Deheubarth in mid Wales . The castle was besieged again by the Welsh in 1187 . Although Llywelyn the Last sacked the town during his campaign to retake South Wales in 1260 , the castle was not captured . In the late 13th century , the castle and the town had become part of the feudal lands of William de Valence , 1st Earl of Pembroke . The French knight , who had been given the peerage for his military services for Henry III in the Second Barons ' War , instigated the building of stone wall s around the town . However the work meant that the defensive role of Tenby Castle was compromised . By the end of the 13th century , the town walls around the old town of Tenby were mostly completed although improvements continued . In 1328 , a D - shaped barbican was added to defend the main gate into the town . Further D - shaped towers were also added to the northern and southern parts of the town walls . By the end of the 14th century , Tenby castle is thought to have been largely abandoned as a defensive fortification and in disrepair . In 1457 , Jasper Tudor agreed to split the costs with the town ' s merchants to refurbish and improve Tenby ' s defences . The dry ditch along the outside the town walls was widened to . Furthermore the walls were heightened with the inclusion of a second tier of higher arrow slits behind a new parapet walk . Additional turret towers were added to the ends of the walls where they abutted the cliff edges . In the mid 16th century , another large D - shaped tower ( " Five Arches " ) was built following fears about a second Spanish Armada . In 1648 during the Second English Civil War , a unit of Royalists under the command of Rice Powell held Tenby Castle for 10 weeks until they were starved into surrendering by Parliamentarian forces . Present day . A few features of the medieval castle remain . A path from Tenby harbour to the top of Castle Hill passes through the main square gateway . From the summit of the promontory is a small tower . A circular walk which was laid out in the 19th century follows the line of the original curtain walls . Tenby Museum & Art Gallery is built on the remains of the castle ' s domestic building , probably the great hall . Although the north gate has been demolished to widen the road , Tenby town walls on the north side are largely complete . The eastern walls and towers remain intact .