E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Pollux.
The horses of Castor and Pollux. Cyll’aros and Har’pagos. Seneca and Claudian give Cyllaros to Castor, but Virgil (Georgic iii.) to Pollux. The two brothers mount it alternately on their return from the infernal regions. Har’pagos, the horse from Harpa’gium in Phrygia, was common to both brothers.
