any date, in the roman calendar.

how the reckoning works

the roman month was not a list from 1 to 31. three days carried a name of their own, and everything else was expressed as a distance to the next one of the three.

kalendae

the 1st of every month. the word calendar comes from it: the calendarivm was the ledger of interest owed, and interest fell due on the kalendae.

nonae

the 5th — except in march, may, july and october, where they fall on the 7th. the name means ninth: counted inclusively, they are the ninth day before the idvs.

idvs

the 13th — except in those same four months, where they fall on the 15th. in the original lunar reckoning they marked the full moon.

the month beside a landmark is an adjective and agrees with it, so the three names take it in the nominative: kalendae martiae, nonae martiae, idvs martiae. that is the form this page prints, the one the dictionaries cite. a roman dating a letter used the ablative instead — kalendis martiis, on the kalends of march.

the count runs backwards, and it is inclusive

an ordinary day does not say how much has passed but how much is left: ante diem, so many days before the next kalendae, nonae or idvs. both ends are counted — the day you start from and the day you arrive at. that is why the number always comes out one higher than a modern reader expects.

for the same reason a.d. ii never appears. the eve has a name of its own: prid., pridie, the day before.

a worked example

march 20 is not called march 20. it is counted toward the kalendae of april: eleven days remain from the 21st to the 31st, plus the 20th itself, plus april 1 — thirteen. hence a.d. xiii kal. apriles. note the consequence: past the idvs, a date already carries the name of the following month.

the three fixed days, month by month

the kalendae are always the 1st. the nonae and the idvs shift two days later in march, may, july and october — the four months that already ran to 31 days in the oldest roman calendar.

what this table does not do

• the leap day. the table shows a common year of 365 days. the julian leap year added no new date at the end of february: it counted a.d. vi kal. martias twice — the bis sextum that gave bissextile its name.
• the pre-julian calendar. before the julian reform (in force from 1 january 45 bce) the roman year ran to 355 days plus an intercalary month that the pontifices inserted, or did not, as it suited them. a date earlier than that reform does not translate with this table.
• the years. rome did not count years from a fixed epoch: it named each year after the two consuls in office. the ab vrbe condita count — from the founding of the city — was largely a scholars’ convention, and this page does not compute it.