Castor 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, the other being Pollux, named after the Gemini twins of Roman mythology. Castor's peak is at an elevation of 4,225 m, and it lies between Breithorn and the Monte Rosa. It is separated from Pollux by a pass …Castor 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, the other being Pollux, named after the Gemini twins of Roman mythology. Castor's peak is at an elevation of 4,225 m, and it lies between Breithorn and the Monte Rosa. It is separated from Pollux by a pass at 3,847 m, named Passo di Verra in Italian and Zwillingsjoch in German.