Newcastle Emlyn Castle (Welsh: Castell Newydd Emlyn) is a ruined castle in the market town of Newcastle Emlyn in Carmarthenshire, Wales. It is strategically located on a steep-sided promontory overlooking the River Teifi and was probably built by the Welsh lord Maredudd ap Rhys in about 1240. It changed hands many times over the years in battles between the Welsh and English, and during the English Civil War. The remains of the gatehouse and adjacent towers, and some fragments of wall are all that remain visible now.