Roman Calendar

By the period that TAG represents in the 1st and 2nd centuries AD, the Roman Calendar is very similar to the calendar we use today. Originally the Roman Calendar consisted of only 10 months with either 30 or 31 days in them. This was changed around 710 BC to a twelve month lunar calendar (ie based on the phases of the moon). As it took on average 29.5 days between one new moon and the next, the twelve month lunar year lasted 355 days, with the twelve months having between them 28 and 31 days. Every other year a whole extra month (which alternated between 22 days and 23 days) was inserted after the 23rd day of February, which was the shortest month with only 28 days, to try to keep the calendar in line with the solar year of approximately 365 days.

The next major change to the Roman Calendar came in 46BC when Julius Caesar decided to abandon the Lunar year in favour of a Solar year of 365.25 days, this being due to the fact that the Calendar was in such a mess with all the intercalations (adding extra periods) that it had drifted away from the seasons. The year was now defined as 365 days with an extra day added every fourth year to February, but due to some adminstrative error the extra day was added every third year and was not discovered until 9BC when Augustus was Emperor. He promptly suspended the leap years until the Earth caught up with the calendar.

After the assassination of Julius Caesar the Senate decided to honour him by declaring that the seventh month, called Quintilis, should be renamed Julius, and in 8 BC the Senate also decided to honour the Emperor Augustus by renaming the month Sextilis after him.

Every Roman month contained three days of particular importance, these were the Kalends, the Nones and the Ides.

  • The Kalends Occurred on the first day of every month.
  • The Nones always Occurred nine days before the Ides, on either the 5th or 7th of the month.
  • The Ides Occurred on the 15th day of every month which contained 31 days, and the 13th day of all other months.
All other dates were calculated by counting backwards inclusively from these established days, ie the 11th July would be "5 days before the Ides of July".

The Roman year was named after the two Consuls elected for that period, and the Roman calendar counted the years ab urbe condita or "from the founding of the city".