The Welsh monk Nennius, writing in the 9th century, recorded the name as Cetgueli - the earliest spelling on record. What it means has been argued for centuries. One reading takes it as the kingdom of a forgotten chieftain called Cadwal. Another sees the Welsh words Cyd and Gweli, joint bed, describing the way the town sits at the confluence of two rivers, the Gwendraeth Fawr and the Gwendraeth Fach. Local legend adds a third tradition: the 5th-century chieftain Cunedda is said to have invaded the area and been killed and buried at a hill just north of town that still bears his name, Allt Cunedda. Welsh place-names are often archaeological objects in their own right, layered with claims and counter-claims you can still hear locals defend in the pub.

The Normans came to Kidwelly in the early 12th century and threw up a motte-and-bailey of earth and timber on the north bank of the Gwendraeth Fach. In the 13th century, as part of Edward I's ring of steel for controlling Wales, the wooden fort was rebuilt in stone according to the latest military thinking: a concentric castle with one ring of walls inside another, so the inner ward could hold even if the outer fell. The great gatehouse, begun in the late 14th century, was not finished until 1422 - over thirty years of masonry to defend a single doorway. In 1403 the castle was besieged by forces loyal to Owain Glyndwr during his rebellion for Welsh independence. The walls held. They are still holding, and Kidwelly Castle today is among the most complete and dramatic medieval fortresses surviving anywhere in Wales.

Gwenllian was the daughter of Gruffudd ap Cynan, prince of Gwynedd, and sister of Owain Gwynedd. She married Gruffydd ap Rhys of Deheubarth - the Welsh prince whose grandfather had ruled all of southwest Wales before the Norman conquest. In late 1135 Gruffydd travelled north to seek alliances against the Norman lords pressing into Welsh territory. While he was away the Lord of Kidwelly, Maurice de Londres, moved against his lands. Gwenllian raised what forces she could and rode out to meet him. She brought two of their sons - Maelgwyn and Morgan - with her. The Welsh chronicles say she fought with the courage of a champion. The Welsh chronicles also say she lost. Maurice's men took her prisoner and killed her on the field, possibly beheaded her; Morgan died beside her. Maelgwyn died in custody. For her contemporaries she was something rare - a woman who had led men into battle. The Welsh remembered.

Industry came late to Kidwelly. A tinplate works was set up just north of the town in 1737, only the second such works in Britain, and the trade gradually transformed the place from a quiet market town into a working one. The works ran for two centuries before closing in 1941, and the surviving buildings became the Kidwelly Industrial Museum until that too closed in 2017. The town also produced a darker kind of fame in 1919, when Mabel Greenwood died of what the post-mortem found to be arsenic poisoning. Her husband Harold, a local solicitor, was tried for murder at Carmarthen assizes the following year. The jury acquitted him while simultaneously declaring that they believed his wife had been deliberately poisoned - a verdict so peculiar it made the Greenwood case a fixture in Edwardian true-crime collections for the next half-century. Harold remarried and left.

Kidwelly has 3,689 residents, a fourteenth-century town gate and bridge, a quay that has become a nature reserve, and a rugby club founded in the 1880s that produced Ray Gravell, the rugged centre who won 23 caps for Wales. The West Wales Line runs through, with trains east to Swansea and Cardiff, west to Pembroke Dock and Fishguard. Three miles east lies Pembrey Circuit, where rally drivers and racing cars whine through Sunday afternoons on the runways of a former RAF airfield. The Princess Gwenllian Community Centre sits on Hillfield Villas, named for the woman buried somewhere in a field beyond the woods. The castle holds the skyline. The estuary holds the silence.