Castle an Dinas is an Iron Age hillfort at the summit of Castle Downs near St Columb Major in Cornwall, UK (grid reference ) and is considered one of the most important hillforts in the southwest of Britain. It dates from around the 3rd to 2nd century BCE and consists of three ditch and rampart concentric rings, above sea level. During the early 1960s it was excavated by a team led by Dr Bernard Wailes of the University of Pennsylvania during two seasons of excavation.