Roman Calendar - Months

Months

In the earliest times the three reference dates were probably declared publicly, when appropriate lunar conditions were observed. After the reforms of Numa, they occurred on fixed days.

• Kalendae (whence "calendar"), Kalends—first day of the month; it is thought to have originally been the day of the new moon. According to some ancient or modern proposed etymologies of the word, it was derived from the phrase kalo Iuno Covella or kalo Iuno Novella, meaning respectively "hollow Juno I call you" and "new Juno I call you", an announcement about the Nones or in proclaiming the new moon that marked the Kalends which the pontiffs made every first day of the month on the Capitoline Hill in the Announcement Hall.
• Nonae, Nones—thought to have originally been the day of the half moon. The Nones was eight days before the Ides, and fell on the 5th or 7th day of the month, depending on the position of the Ides. (Nones implies ninth from the Latin novem, because, counting Ides as first, one day before is the second, and eight days before is the ninth).
• Idus, Ides—thought to have originally been the day of the full moon, was the 13th day of the months with 29 days, but the 15th day of March, May, July, and October (the months with 31 days).

The day preceding the Kalends, Nones, or Ides was Pridie, e.g. Prid. Id. Mart. = 14 March. Other days were denoted by ordinal number, counting back from a named reference day. The reference day itself counted as the first, so that two days before was denoted the third day. Dates were written as a.d. NN, an abbreviation for ante diem NN, meaning "on the Nth (Numerus) day before the named reference day (Nomen)", e.g. a.d. III Kal. Nov. = on the third day before the November Kalends = 30 October. The value 2 was not used to denote a day before the fixed point, because second was the same as pridie. Further examples of date equivalence are: a.d. IV Non. Jan. = 2 January; a.d. VI Non. Mai. = 2 May; a.d. VIII Id. Apr. = 6 April; a.d. VIII Id. Oct. = 8 October; a.d. XVII Kal. Nov. = 16 October.

Some dates were sometimes known by the name of a festival that occurred on them, or shortly afterwards. Examples of such dates are recorded for the Feralia, Quirinalia and the Terminalia, though not yet for the Lupercalia. These dates are all after the Ides of February, which suggests that they are connected with resolving an ambiguity that could arise in intercalary years: dates of the form a.d. Kal. Mart. were dates in late February in regular years but were a month later in intercalary years. However, it is much debated whether there was a fixed rule for using festival-based dates. It has been variously proposed that a date like a.d. X Terminalia (known from an inscription in 94 BC) implied that its year was, was not, or might have been intercalary.

When Julius Caesar added days to some months, he added them to the end of the month, so as not to disturb the dates of festivals in those months. This increased the count of all days after the Ides, and had some odd effects. For example, the emperor Augustus was born in 63 BC on the 23rd day of September. In the pre-Julian calendar this is seven days before the Kalends of October (or, in Roman style, counting inclusively, a.d. VIII Kal. Oct.), but in the Julian calendar it is eight days (a.d. IX Kal. Oct.). Because of this ambiguity, his birthday was sometimes celebrated on both dates.