Kidwelly Castle (Welsh: 'Castell Cydweli') is an Norman castle overlooking the river Gwendraeth and the town of Kidwelly, Carmarthenshire, Wales.
The present remains of the castle include work from about 1200 to about 1476. Created as a defence against the Welsh, the castle fell to the Welsh several times in the twelfth century. Later in its history, it was unsuccessfully besieged by forces of Owain Glyndwr in 1403 with assistance from soldiers from France and Brittany who captured Kidwelly town. The castle was relieved by a Norman army after just three weeks. The gatehouse was extensively damaged and it was rebuilt on the instructions of King Henry V. It largely escaped involvement in the English Civil War.
The River has two almost equal branches that have their confluence in their joint estuary at Carmarthen Bay. The Gwendraeth Fawr (Large Gwendraeth in Welsh) is surprisingly the smaller and has its source in a series of springs to the north of Cross Hands.
The Gwendraeth Fach (small Gwendraeth in Welsh) flows further to the north having its source about 4 miles north of Cross Hands near the 190-metre (620 ft) contour at Penrhiwgoch. Passing under the A48 road, it is soon below the 160-foot (50 m) contour, flowing in a south-westerly direction to the south of Llanddarog, Cwmisfael and Llangyndeyrn, before turning southwards through Mynyddygarreg. It reaches the estuary to the west of Kidwelly after passing through the town centre.
The name 'Kidwelly' is thought to be very old: the earliest form of the name, 'Cetgueli', is recorded by the monk, Nennius, writing in the 9th century. The town and castle were established by the invading Normans during the 12th century.
A field in the neighbouring forest of Kingswood, Maes Gwenllian is known as the location of a battle in 1136, in which Princess Gwenllian, sister of Owain Gwynedd, led her husband's troops into battle against a Norman army during his absence. She is believed to have been killed either during the battle or shortly afterwards, historians debate whether her death was at Maes Gwenllian or if she was marched back to Kidwelly Castle to be beheaded there.
Although being an ancient town, Kidwelly grew significantly during the industrial revolution, as did many other towns in South Wales. The town was home to a large brickworks and tinworks. Little evidence now exists of such activities since the closure of the industrial works, with the exception of Kidwelly Industrial Museum.