High Quality Content by WIKIPEDIA articles! Caernarfon Castle (Welsh: Castell Caernarfon) is a medieval building in Gwynedd, north-west Wales. There was a motte-and-bailey castle in the town of Caernarfon from the late 11th century until 1283 when King Edward I of England began replacing it with the current stone structure. The Edwardian town and castle acted as the administrative centre of north Wales and as a result the defences were built on a grand scale. There was a deliberate link with Caernarfon`s Roman past – nearby is the Roman fort of Segontium – and the castle`s walls are reminiscent of the Walls of Constantinople.