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