The Roman Calendar - Brief History | Calendar Table

The Roman Calendar – Brief History

The Roman calendar is also known as the pre-Julian calendar and it was supposedly invented by Romulus, Rome’s first king. The calendar used a system of months and celebrated special days in each month. As different gods were held in high esteem in different geographical regions, there were several variations of this calendar throughout different regions.

Roman Calendar Background

The calendar consisted of 10 months and started with the month of March or Martius. Each month had either 30 or 31 days and 61 days were unaccounted for during the winter. Tradition says that roman ruler Numa Pompilius later added the months of January and February to this calendar.

The year consisted of 304 days in total before the winter months of January and February were added to the calendar. The general Roman calendar was used since the founding of Rome until the fall of the Roman Empire.

Components and Importance of the Roman Calendar

The first month of the Roman Calendar began at the same time as the spring equinox and had six months which had 30 days and four months which had 31 days. The ancient Roman calendar marked special days using three categories, the Ides, the Nones, and the Kalends. In the beginning, the month and the special markers were based on the moon, meaning that months were the length of a full lunar cycle.

A priest known as a pontifex had the duty of observing the sky and announcing the appearance of the full moon. This signaled the beginning of a new month. Romans started to separate their months from the lunar cycle around the fifth century B.C.E. Around that time, they began assigning fixed dates to the Kalends, Nones, and Ides.

  • Kalends –the Kalends always represented the first day of the month. The original meaning is considered to have been the day of the new moon.
  • Nones –the Nones fell either on the 5th or on the 7th day of each month. They are thought to have originally represented the day of the half-moon.
  • Ides –the Ides were on the 15th day of the months March, May, July, and October. It fell on the 13th day for the other six months.

Even after the addition of January and February, the Roman calendar remained flawed. Many attempts were made to rectify the issue of remaining days, including adding an extra month in some years, but all failed to solve the problem. These extra months were known as intercalary months and were used to correct the calendar until Julius Caesar reformed it and removed them.

Although it is no longer used nowadays, the Roman calendar had an important contribution to the very calendar we use today. The 12-month calendar that we are all familiar with now is based in the 12 months that the Roman calendar eventually acknowledged.

roman calendar


How Does the Roman Calendar Work?

The special days marked in the Roman calendar were the Kalends, the Nones, and the Ides. Holidays were usually paired together and the rest of the days were considered regular work days. Each day was identified using a series of letters and names. For example, the 9th day of the month was considered the market day and was attributed a letter to mark it as such.

Days were also attributed letters to indicate whether legal action was allowed to take place or not during a certain date. Special letters and names were also used to mark religious holidays, celebrations, and days that served a different purpose than regular workdays.

  • The letter F –days were marked with the letter F to signify that they were “dies fasti” or days on which legal action was allowed
  • The letter N –days marked with the letter N were known as “dies nefasti” or days on which legal action was not allowed.
  • The letter C – days that contained the letter C were days on which citizens could vote on different political or social matters.
  • The letters EN –days that were marked with the letters EN were considered a mixture between C and F days. During these days, the mornings were used for one purpose or activity and the afternoons were destined for another.

Leap Years in the Roman Calendar

The Intercalary months were used in the Roman calendar to reconcile any differences between the calendar and the solar year. If there were any days left in the year, they would be counted at the end of the calendar.

As January and February were the last months to be added to the Roman calendar, which began with the month of March, the end of the Roman year was considered to be on the last day of February which, to the Romans, was February the 23rd. As such, any leap year would be observed by adding more days after the last day of February.

This practice still reflects in modern days, as we observe leap years by adding an extra day to the month of February as well. Because our modern calendar counts 28 days in February during non-leap years, we consider leap day to be the 29th of February. According to the Roman calendar, the leap day would have been February the 24th instead.

Drawbacks of the Roman Calendar

A modern version of the Roman calendar is still being used today, with the names of the months and 31 and 30 day months surviving the test of time. However, there was much confusion because of the original system that the calendar was based on before the leap cycle was stabilized as the varying number of extra days could confuse the definition of “leap year” versus “non-leap year”.


Although the old Roman calendar was often a flawed system, it was used as an inspiration for the calendar that we are using today. The Gregorian calendar, the one currently in use, is a refined version of the Julian calendar that Julius Caesar modified during his reign. Although the Gregorian calendar managed to establish a better system for defining leap years, it was based on the structure that the Roman calendar had already contained.

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