Cefn Carnedd Hillfort is located on a prominent ridge overlooking the confluence of the Severn, Trannon, Cerist and Carno rivers 2km south west of Caersws. It has extensive views of the Severn valley and adjoining tributary valleys.
The hillfort enclosure and outer defences extend just over half a kilometre in length and 120 metres wide. There is a complex multi-phase system of defences enclosing the weaker northern side and the approaches to the gates on the south west, north east and north west sides. The earliest univallate enclosure was located at the south west end and defended by double banks and ditches at the SW and NE ends. The hillfort was then expaned to the north east twice with additional defences. An outer enclosure was added outside the north-eastern defences on the north slope. A possible post Roman defensive bank and ditch was cut across the hillfort interior at an unknown date.
The hillfort has been listed as a candidate site of the last stand of Caratacus in the mid first c. AD