Dinas Rock is a high promontory of Carboniferous Limestone which rises between the Afon Mellte and its left-bank tributary, the Afon Sychryd on the border between the county of Powys and the county borough of Neath Port Talbot in south Wales. It can be found near the village of Pontneddfechan near Glyn Neath at the head of the Vale of Neath. It derives its name from the presence of Iron Age earthworks on its summit, dinas in Welsh signifying a defensive site or "city".