The History of Rome (1.19.5-1.20.2)

But, as this would fail to make a deep impression without some claim to supernatural wisdom, he pretended that he had nocturnal interviews with the nymph Egeria: that it was on her advice that he was instituting the ritual most acceptable to the gods and appointing for each deity his own special priests.

First of all he divided the year into twelve months, corresponding to the moon's revolutions. But as the moon does not complete thirty days in each month, and so there are fewer days in the lunar year than in that measured by the course of the sun, he interpolated intercalary months and so arranged them that every twentieth year the days should coincide with the same position of the sun as when they started, the whole twenty years being thus complete.

He also established a distinction between the days on which legal business could be transacted and those on which it could not, because it would sometimes be advisable that there should be no business transacted with the people.

Next he turned his attention to the appointment of priests. He himself, however, conducted a great many religious services, especially those which belong to the Flamen of Jupiter.

[*] But he thought that in a warlike state there would be more kings of the type of Romulus than of Numa who would take the field in person. To guard, therefore, against the sacrificial rites which the king performed being interrupted, he appointed a Flamen as perpetual priest to Jupiter, and ordered that he should wear a distinctive dress and sit in the royal curule chair. He appointed two additional Flamens, one for Mars, the other for Quirinus, and also chose virgins as priestesses to