How the Roman calendar worked
Romans did not number the days of a month from 1 upward. They counted backwards to three fixed points:
- Kalends (Kal.): the 1st of every month.
- Nones (Non.): the 7th in March, May, July and October; the 5th in other months.
- Ides (Id.): the 15th in March, May, July and October; the 13th in other months.
The day before one of these is pridie (pr.). Other days are written ante diem (a.d.) plus a number, counted inclusively, so both the start day and the target day count. November 16 is therefore a.d. XVI Kal. Dec., the sixteenth day before the Kalends of December.
In leap years February 24 was doubled (bis sextum), which is where the word "bissextile" comes from.
Each date page on this site shows its Roman date, worked out with these rules for the Julian calendar.
LATIN LINE OF THE DAY
Sunt bona, sunt quaedam mediocria, sunt mala plura quae legis hic.
“Some are good, some middling, more are bad, of what you read here.”