Herakles with them when they set out to plant colonies in Southern Italy, so the heavy-mounted horsemen carried their god Castor with them wherever they went.  The Italic tribes in their turn were quick to seize upon this idea of cavalry, and with it as an essential part went its divine patron, Castor.  Thus the Castor-cult moved steadily northward, carried, as it were, on horseback.  At last it reached Latium, and there the little town of Tusculum, afterwards so famous as the residence of Cicero, became in some unaccountable way an important cult-centre, and did for Castor what Tibur had done for Hercules, i.e. latinised him, so that Rome received him not as an alien but as one of her kin.  There can be little doubt that the Roman cult actually did come from Tusculum, and that in its introduction into Rome, as in every other step on its march, it was connected with the reorganisation of the cavalry.  This would seem to imply that Tusculum was famous for its cavalry and that Rome took the idea of it from her—­statements for which we have unfortunately no other confirmation, though we have abundant proof of the cult at Tusculum and of Rome’s close association with it.

Castor was thus the patron of the “horsemen” (equites) and his great day was July 15, when the horsemen’s parade took place.  Possibly this had been the date of the festival at Tusculum, a day especially appropriate because it was the Ides of the month, and the Ides were sacred to Juppiter, whose sons Castor and Pollux (Dios-kouroi) were supposed to be.  It is extremely interesting in the light of this knowledge of the true state of affairs to see how legend later explained the coming of Castor and Pollux.  It was an incident in the mythical war which was supposed to have taken place after the last Tarquin had been driven out, and the republic had been started.  The adversaries of Rome, allied with Tarquin, notably Octavius Mamilius of Tusculum, fought against the Romans in the battle of Lake Regillus on July 15, B.C. 499.  The Romans won, and the first news of victory was brought to Rome by the miraculous appearance of Castor and Pollux who were seen watering their horses in the Forum at the spring of Juturna.  A temple on this spot was then vowed and fifteen years later, B.C. 484, it was completed and dedicated.  Tusculum, July 15, and the dedication of the temple in B.C. 484 are seemingly the only historical facts in this legend; and long before B.C. 499 Castor was worshipped in Rome, especially on July 15.  The site of his original worship was without doubt the same locality in the Forum where his temple was subsequently built, for it is an almost invariable rule that the earliest temples are built on the actual site of, or close to, the old altar or shrine which preceded the formal temple.  Like Hercules therefore he was received inside the pomerium, and probably for a similar reason, because it was felt that he was a god of Tusculum, and hence a god of Rome’s