Plutarch Numa 19

[1] That the Romans had at first only ten months in their year, and not twelve, is proved by the name of their last month; for they still call it December, or the tenth month. And that March used to be their first month, is proved by the sequence of months after it; for the fifth month after it used to be called Quintilis, the sixth Sextilis, and so on with the rest. Therefore, when they placed January and February before March, they were guilty of naming the above-mentioned month Quintilis, or fifth, but counting it seventh.

[2] And besides, it was reasonable that March, which is consecrate to Mars, should be put in the first place by Romulus, and April in the second place, since this month is named after Aphrodite. In it they sacrificed to this goddess, and on its first day the women bathe with myrtle garlands on their heads. Some, however, say that April, with its smooth p, cannot be derived from Aphrodite, with its rough ph, but that this month of high spring time is called April because it opens and discloses the buds and shoots in vegetation, this being the meaning of the word aperio.

[3] The next month in order is called May, from Maia, the mother of Mercury, to whom it is sacred; and June is so named from Juno. There are some, however, who say that these months get their name from an age, older and younger; for majores is their name for the elder, juniores for the younger men. Each of the remaining months they named from its arithmetical position in the list, the fifth Quintilis, the sixth Sextilis, and so on with September, October, November, and December.

[4] Afterwards the fifth month was named Julius, from Julius Caesar, the conqueror of Pompey; and the sixth month Augustus, from the second Caesar, who was given that title. The seventh and eighth months bore for a short time the names Germanicus and Domitianus, which the emperor Domitian gave them; but when he was slain, they resumed their old names of September and October. Only the last two months, November and December, preserved the names derived from their position in the list just as they were at the outset.

[5] Of the months which were added or transposed by Numa, February must have something to do with purification for this is nearest to the meaning of the word, and in this month they make offerings to the dead and celebrate the festival of the Lupercalia, which, in most of its features, resembles a purification. ¹ The first month, January, is so named from Janus. And I think that March, which is named from Mars, was moved by Numa from its place at the head of the months because he wished in every case that martial influences should yield precedence to civil and political.

[6] For this Janus, in remote antiquity, whether he was a demi-god or a king, was a patron of civil and social order, and is said to have lifted human life out of its bestial and savage state. For this reason he is represented with two faces, implying that he brought men’s lives out of one sort and condition into another.