Roman Calendar

The Roman calendar changed many times over the years and between the foundation of Rome and when Rome fell as an empire.

The calendar that was used before 46 B.C. is called the pre-Julian calendar and the calendar used after 46 BC was called the Julian calendar.

Lunar Calendar

The first calendar was only ten months long and it started at the vernal equinox.

This calendar was invented by Romulus who founded Rome in the year 753 BC.  The first calendar was based on the Greek calendar.


The ten months of the pre-Julian calendar were:

  • Martius which had 31 days.
  • Aprilis which had 30 days.
  • Maius which had 31 days.
  • Quintillis which had 31 days.
  • Sextilis which had 30 days.
  • September which had 30 days.
  • October which had 31 days.
  • November which had 30 days.
  • December which had 30 days.

304 Days

The pre-Julian calendar had 304 days, and this included there to be 61 winter days and there was no season of fall that took place on the calendar.


The first changes that happened on the calendar were changed by Numa Pompilius.

He was the second King of Rome and he changed the calendar from 30 day months to 29 days and then he decided to add January and give it 29 days and February and gave it 28 days.

The change by Numa Pompilius happened in 713 BC and made the calendar have 355 days.

Solar Year

The calendar needed to work with the solar year and so a leap month of 27 days known as the Mensis Intercalaris or the Mercedonius was added to the month of February which shortened the days from 27 to 23 or 24 days.

This made there be 377 or 378 days per year.

The idea to have an intercalary month (Leap year) was changed by Pontifex Maxiumus who was the high priest of the Roman religion.

Second Punic War

The first time that the intercalary months was broken down happened during the Second Punic War which was led by Lex Acilia and this happened in 191 BC.

No one is really sure what changes were made but they helped line up the days.

First Century

The second time that the intercalary months were broken down happened during the First Century BC and the change brought about the Julian calendar which came about from Julius Caesar.

Phases of the Moon

There were 3 specific days each month that was based on the phases of the Moon and these days were declared only when the conditions of the moon were right but after the changes from Numa Pompilus they happened on fixed days, no matter what the moon conditions were.


The Kalends were the first day of the month and this was called Kalends which is from the word calendar.


Depending on which month this was, the day would be different and would fall mostly when there was a half moon.

This would usually be on the 5th or on the 7th day of that month.


Once again, depending on which month it was, this day could fall on the 13th or the 15th day of the month.  The months for this were either March, May, July or October.


In the Roman Republic, they did not count the years, they only named a year after the consuls but later, they begin to count the years starting with when Rome was founded.

Modern Calendar

The modern calendar or the Western calendar is different than the pre-Julius counter.

The days were numbered differently because the Romans did not count the days of the month in order but they counted them so when they would say the 2nd of September, it would mean that it was 4 days before the 5th of September instead of it being 3 days before.

With the modern calendar, we count our days in order 1-31 or however many days are in the month.

Facts About the Ancient Roman Calendar

  • The Ides of the Nones was said as a mnemonic which went: In March, July, October, May, The Ides falls on the 15th  The Nones of the 7th.  The rest besides take 2 days less, for Nones and Ides.
  • The Romans used the abbreviations such as A.D. which meant ante diem or the day before.
  • When Julius Caesar added a day to the month of September, he didn’t add it to the end but he added it to the day after the Ides which was September 14th.
  • The Romans used eight days as a week which was called market week.
  • The market day was a day when people would travel to the city.
  • Comitia was a law that was given by Lex Hortensia which did not allow there to be elections on market days, only legal actions.
  • There was a superstition that it was unlucky to start a year when it was market day and so whoever wrote the calendar would change it so that this would not happen.
  • 7-day weeks changed during the Imperial period after the Julian calendar was made.
  • Days of the week were dedicated to the names of gods.
  • Sunday was called the day of the sun named Dies Solis.
  • Monday was the day of the moon named Dies Lunae
  • Tuesday was the day of Mars called Dies Martis
  • Wednesday was the day of Mercury called Dies Mercuri.
  • Thursday was the day of Jupiter called Dies lovis.
  • Friday was the day of Venus called Dies Veneris.
  • Saturday was the day of Saturn and called Dies Saturni.

What did you learn?

  1. What is the Roman calendar?  The Roman calendar is a calendar that is different than our calendar today.  It was called first the pre-Julian calendar and then the Julian calendar.
  2. What is the biggest difference between the calendar today and the Roman calendar? The biggest difference is that the pre and Julian calendar did not have the same number of days as our calendar does.
  3. What were the names of the week named after? The names of the week were named after Roman gods.
  4. Who added days in September and who was the calendar named after? The calendar was named after Julius Caesar who would add dates according to the Ides.
  5. How many days were in the pre-Julian calendar? The first calendar had 304 days.
  6. What season was not in the calendar? The season of fall was not in the calendar and there were 61 days of winter.