The Ancient Roman and Julian Calendars

This shows the months as Ianuarius (29 days), Februarius (29), Martis (31), Aprilis (29), Maius (31), Iunius (29), Quintilis (31), Sextilis (29), Sepembris (29), Octobris (31), Novembris (29) and Decembris (29). The last column is the intercalary month, with 27 days, that was added when required, as the normal year only had 356 days, nine short of a standard year.

As time went on, the calendar went into a state of disarray, as the intercalary month was often not added when it should have been, or added more than once, in order to satisfy superstitions or lengthen the years, which were named after the current leaders of Rome, to suit personal ambitions. Eventually, Julius Caesar reformed the calendar, basing it on the Egyptian solar calendar of 365 days, and introduced the leap year of 366 days every four years to keep it in synchronisation with the solar year. The months now had the same number of days at it has to this day.

After Caesar's death, the month of Quintilis was renamed Iulius (July) in his honour. Unfortunately, the authorities made an error with the application of the leap years, applying it every three years instead of four. To correct the error, Augustus Caesar dropped some subsequent leap years, and Sextilis was renamed Augustus in his honour.

In the Roman calendar, however, the system of counting days was very different. The months contained three primary markers - the Kalends, the Nones and the Ides. The Kalends were always the first day of the month. The Nones were on the 5th of the month and the Ides on the 13th, except in March, May, July and October, when they fell on the 7th and 15th respectively (note that these months were the ones that had 31 days in the original calendar). The days in between were numbered by counting down towards the next marker day. This was done inclusively, so the 11th January was the "third day before the Ides" and the 12th was the "day before" (Pridie), etc. All the days after the Ides were numbered by counting down towards the next month's Kalends, so the 15th February was actually called the 15th day before the Kalends of March. The following table shows how this worked, using the first three months of the year as an example.

This system was used for centuries afterwards, and it was only around the 11th to the 13th centuries that our current system of numbering from 1 to 28, 29, 30 or 31 really came into widespread use.