The Roman Calendar

The Roman system of measuring days, weeks, months, and years is very similar to our modern system with a few exceptions.

The Romans dated their years by the year in office of the consuls starting after the fall of the monarchy in 509 BCE. A similar method was used by the Egyptians, who took their years from the reign of the Pharaoh. This method was fairly unreliable before the 4th century BCE, as many local systems were also used in different areas, and they do not always match up with one another. An alternate method of figuring years was by counting from the founding of Rome (A.U.C. -- anno urbis conditae). By our current reckoning this occurred in 753 BCE.

The Roman Calendar during the Republic was based on the lunar cycle. Starting around the 500s BCE, it had twelve months with differing numbers of days, that, when added together, gave a year that was 355 days long. 22 or 23 days were added to every other February to make up the difference. Ianuarius was not made the first month of the year until the mid-second century BCE.

Republican Calendar
Month Number of Days
Ianuarius 29
Februarius 28 / 40 / 41
Martius 31
Aprilis 29
Maius 31
Iunius 29
Quinctilis 31
Sextilis 29
September 29
October 31
November 29
December 29

By Julius Caesar's time the calendar was about three months ahead of the solar calendar, so Caesar made 46 BCE 445 days and then decreed that the following years would be 365 days with an extra day added to February every three years (Augustus changed this to every four years). Caesar also renamed Quinctilis to Iulius (after himself). Augustus renamed a month after himself as well, changing Sextilis to Augustus.

Julian Calendar
Month Number of Days
Ianuarius 31
Februarius 28 / 29
Martius 31
Aprilis 30
Maius 31
Iunius 30
Iulius 31
Sextilis 31
September 30
October 31
November 30
December 31

Weeks as we know them today did not exist for the Romans. Every nine days was a market day (nundinae), and it was on that day that citizens would take their produce into the city to sell it. A seven day period was not used in the Empire after Christianity gained popularity, and is based on the Jewish calendar.

The Romans did not number the days in their months like we do today (i.e. January 5th); instead, they counted them as days before the three named days: The Kalends, The Nones, and the Ides. The Kalends are the first day of every month (the new moon). The Nones are the date of the 1st quarter moon, which corresponds to the 5th or 7th day of the month, depending on how many days that month had. The Kalends are the date of the full moon, or the 13th or 15th day of the month.

Each day of the year was catagorized as either comitialis (lucky days when the popular assembly could meet), fastus (regular days) or nefastus (unlucky days when nothing new should be started--religious feasts often occurred on them). Some days were so unlucky that nothing (including religious observances) should be done on them. A few days were both lucky and unlucky, depending on the time of day.

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