I have been told that Kalendae is the first day of a month. However, the Latin dates — which was discussed in this other question — alone do not make this obvious. Dates are expressed by comparison to three special days every month: Kalendae, Nonae, and Idus.

Based on everything I know about the Roman calendar, it would make sense that Idus was actually the last day of a month. Or perhaps days between Idus and the following Kalendae belong to no month at all. Or maybe a month consists of the three special days and other days have to be expressed in relation to these interesting days because other days belong to no month at all. It is not obvious that every day should be part of some month.

Is it clearly stated somewhere in ancient literature that Kalendae is the first day of a month? Is there some ancient source describing the structure of a month in this sense? Evidence from inscriptions is also welcome if it sheds some light on the matter. There seems to be a very strong modern consensus that Kalendae is the first day, but I realized that I know no reason for this.

  • I think you are not denying that chronologically kalendae januarii is the same day that we would now call the 1st of January (Julian). You are asking whether the Romans actually considered the kalendae to mark the beginning of the month. Am I right? In this case, jknappen's answer is not relevant.
    – fdb
    Commented Nov 11, 2016 at 15:22
  • @fdb, you are right. I agree that Kal. Jan. was what we know as January the first. The question is whether the boundaries between different months have moved.
    – Joonas Ilmavirta
    Commented Nov 11, 2016 at 15:29
  • @fdb May I point out that the names of months are adjectives? So we have mensis ianuarius, kalendae ianuariae and so on.
    – Tom Cotton
    Commented Nov 11, 2016 at 16:24
  • @TomCotton. I think Januarius is used both as an adjective and as a noun. perseus.tufts.edu/hopper/…
    – fdb
    Commented Nov 11, 2016 at 17:01

2 Answers 2


In classical times the seven-day week was unknown; obviously, there could be no named days of the week to use as reference points. Months at least were of specified lengths, but the actual date was described by a clumsy method which depended on three datum points within the month itself. These points were the Kalends, Nones and Ides, which occurred in that order.

Dates were calculated by counting backwards from these datum points: that is to say, they were expressed as, for example, the third day before the Nones of January, the fourth day before the Ides of March, and the seventh day before the Kalends of November.

By long tradition, the Kalends were the first day of a month. There are many ways of demonstrating this, but one of the best authorities is the poet Ovid’s poetical treatise on the Roman calendar. It was written in strict chronological order, beginning in Book I with the first of January, which he calls the Kalends of January, named after Janus:

Ecce tibi faustum, Germanice, nuntiat annum / inque meo primus carmine Ianus adest.

Dates follow in the sequence identified first, by the Nones, secondly, by the Ides, and finally by counting back from the next Kalends — of February.

Book II begins:

Ianus habet finem. Cum carmine crescit et annus: / alter ut hic mensis, sic liber alter eat.

This leaves no room for doubt that the Kalends mark the first day of a month.

  • 1
    I agree. Ovid's Fasti is decisive.
    – fdb
    Commented Nov 11, 2016 at 16:56

First point, the meaning of the Latin dates was never forgotten but traded continously (e.g. by the Roman Catholic church) into our times.

A second point is that we are able to verify some dates referring to astronomical events (e.g., solar eclipses) independently. Using such methods helped in falsifying the Phantom time hypothesis (aka Erfundenes Mittelalter.

  • I did not actually ask whether Kalendae Ianuariae were on the same day as January 1. (That confirmation is interesting though. +1.) The questions is whether Kalendae marked the beginning of the month, or in other words, whether boundaries between different months have moved since antiquity.
    – Joonas Ilmavirta
    Commented Nov 11, 2016 at 15:32
  • @JoonasIlmavirta To clarify, your question is why (and whether) "a.d.XIX.Kal.Ian." was regarded by the Romans as part of December rather than January, right?
    – Random832
    Commented Nov 11, 2016 at 21:12
  • @Random832, yes, that is one way to phrase it. (Or perhaps it was not regarded part of either month.)
    – Joonas Ilmavirta
    Commented Nov 11, 2016 at 21:46

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