Harlech Castle, located in Harlech, Gwynedd, Wales, is a concentric castle, constructed atop a cliff close to the Irish Sea. Architecturally, it is particularly notable for its massive gatehouse. Built by King Edward I during his conquest of Wales, the castle was subject to several assaults and sieges during its period of active use as a fortification. The castle served as the de facto capital of an independent Wales between 1404 and 1409 when it was held by Owain Glyndŵr.