Castor (Italian: Castore) is a mountain in the Pennine Alps on the border between Valais, Switzerland and the Aosta Valley in Italy. It is the higher of a pair of twin peaks (Zwillinge), the other being Pollux, named after the Gemini twins of Roman mythology. Castor's peak is at an elevation of 4,228 m (13,871 ft), and it lies between Breithorn and Monte Rosa.