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Ancient Roman Calendar: Evolution & History

Joseph Comunale, Christopher Cudabac
  • Author
    Joseph Comunale

    Joseph Comunale obtained a Bachelor's in Philosophy from UCF before becoming a high school science teacher for five years. He has taught Earth-Space Science and Integrated Science at a Title 1 School in Florida and has Professional Teacher's Certification for Earth-Space Science.

  • Instructor
    Christopher Cudabac

    Chris has taught World History and Cultures at the High School level and has a master's degree in Classics.

Learn about the ancient Roman calendar. Explore the months and days of the week, who had the authority to change the calendar, and how the Roman calendar evolved. Updated: 03/24/2022

Ancient Roman Calendar

The calendars and date keeping implemented by Julius Caesar and emperor Augustus are often associated with the Roman calendar. However, the original ancient Roman calendar was quite different than the later Roman calendars, especially the modern calendar used today. There are some similarities. For example, the names of the months are somewhat familiar: Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, and December. But there are also notable differences.

For starters, the original ancient Roman calendar in prehistory was likely based on the observational lunar cycles and calendar. A month would have begun at the first signs of a new lunar cycle; i.e., a new crescent moon. A new crescent moon is a crescent moon that follows a new moon (waxing). Each lunar cycle and, therefore, each month is essentially 29.5 days long. However, with the adjustment using the Sun as a guide for days, each month would either be 29 or 30 days long. This puts the calendar year 10 to 11 days shorter than the true solar year, a peculiarity that will be discussed later in the lesson.

Additionally, the ancient Roman writer Marcobius recorded for historians another possible calendar that was implemented by the king named Romulus. This calendar consisted of 10 months. The start of the year began in spring with March and continued through summer and fall, stopping in December. Six of these months were broken up into 30 days, and four of them consisted of 31 days. This put the calendar year at 304 days.

It should be noted that the months weren't counted as they are today. Because the months were signaled by the moon, they were navigated with references to the kalends, nones, and ides. The term kalends refers to the first sighting of the new crescent moon, the nones references the first quarter moon of the month, and the ides refers to the full moon. The Romans would also count down to the next lunar sighting. So, instead of navigating each month by referencing a numerically labeled date such as April 1st, the Romans would say the kalends of April. April 5th would be the nones of that month, April 2nd becomes four days before the nones of April, and April 20th becomes ten days before the kalends of May.

Roman Calendar: Days of the Week

An 8-day week was used in early Roman calendars. The week consisted of the days of the week, named after the Sun, Moon, and five visible planets: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday. However, there was an additional market day called the nundinae. This was a sort of resting day for the ruling class, or a day to go to the markets. However, when the calendar attempted to include both 7-day and 8-day weeks, the 8-day week fell out of fashion in favor of the 7-day week because people simply preferred the rhythm of a 7-day week. The 7-day week was officially established as a part of the Roman calendar by Constantine in 321 AD.

Roman Calendar: Months

As previously mentioned, because the ancient Roman calendar navigated each month using visual references to the lunar cycle, both the 12-month and 10-month calendars were still short either a few or many days, respectively. If the calendar year was left short of the true solar year, then the calendar year would quickly fall out of alignment with the seasons. The prehistory Romans avoided any shift of seasonal alignment of the months by having a period during winter where the calendar was temporarily suspended.

During Romulus' 10-month calendar, the year only tracked 304 days. Again, this would have caused the Roman calendar months to quickly fall out of alignment with the seasons. During this version of the Roman calendar, the year still contained some 50 remaining days muddled into the winter season. These muddled days are called an intercalary period, and they were declared by the pontifex maximus, or a sort of chief high priest. However, this high priest could also manipulate the calendar year for political gain. That is, he could lengthen a year during which his political allies were in power and shorten a year in which his enemies had control. This occurred sometimes in Roman history, throwing the calendar year out of alignment with the seasons.

Romulus later added the additional months of January and February, and briefer intercalation occurred within February. Then the new year would begin at the first sign of a new crescent moon at the beginning of March (the kalends of March). Besides the aforementioned subtle changes to the Roman calendar and the Roman days of the week, there have been a few more changes made to the ways dates are kept and tracked.

Introduction

When we modern people study the Roman calendar, we may find its arrangement of days to be absurd. But we can definitely find familiar elements, such as the names of the months. In this lesson, we'll trace the characteristics and history of the Roman calendar, going through its designations for the days, weeks, and months.

Changes to the Roman Calendar

Julius Caesar was involved in changing the Roman calendar. The Julian reform to the calendar (or the creation of the Julian calendar) came after Julius Caesar took up the role of pontifex maximus in 63 BCE.

Julius Caesar changed the calendar so that the months would alternate between 30 and 31 days, but he kept February at 28 days. This established the year that is known to be 365 days. Additionally, Julius Caesar was aware from his studies in Egypt that the astronomers in Egypt had observed and recorded a solar year which was 365.25 days. Because of this, Julius Caesar established the leap year, where every fourth year an additional day is added to the month of February. These changes completely removed the need for intercalary periods. However, the Roman priests did not initially apply the leap years correctly.

Counting the Days

The earliest Roman calendar was based on cycles of the moon, which influenced their method for designating days in a month. The Romans counted down the days to one of three special days: the kalends, nones, and ides. The kalends were the first of the month, coinciding with the new moon; the nones were at the first quarter, and the ides were at the full moon. Later, when the months were disassociated from the lunar cycles, these days were fixed: the kalends on the first of the month, the nones usually on the fifth, and the ides usually on the thirteenth.

Each day in the month was described one of two ways: either as on one of these days ('on the nones of April' was April 5), or by counting down inclusively to the next special day. For example, April 3 was 'three days before the nones of April' (count April 5, April 4, April 3). After the ides had passed, the countdown looked forward to the kalends of the next month: April 14 was, for a Roman, 18 days before the kalends of May.

Days in a Week

Within the month, the Romans used an eight day week that ended in a market day, nunidia. Later, this arrangement lost popularity to the present seven day week.

Above, on this fragmentary Roman calendar, the letters on the left count to the nunidia (H). The numerals count down to the kalends of the next month. The abbreviations on the right show the nunidia (N) and what government business can be done on each day; the smaller text indicates festivals.
ancient Roman calendar

Of Moons and Months

Earliest Roman calendars had ten lunar months, starting with Martius (March), which was the start of the campaigning season and thus sacred to Mars, the Roman war god. Origins for the names of April, May, and June are now unclear. Names for other months came from Latin numbers; for example, decem, 'ten,' provided the name for December, the tenth month of this calendar. About sixty days of winter were left without any designation.

At an early period the Romans formed two months from these nondescript days in winter: January, which was holy to Janus, the god of entrances, and February, which took its name from the Latin verb for purification and atonement. The lunar cycle was dropped, and most months alternated between 29 or 31 days; because of its gloomy associations, February was set at 28 days, providing a year of 355 days.

In the second century BCE, the Romans moved the start of the year to January, so that the magistrates, who assumed office at the year's beginning, could get to far-flung armies before the start of the campaigning season.

Measuring the Year

Even the earliest Romans knew that the solar year was longer than 355 days, so the the chief priest of Rome and keeper the official calendar, the pontifex maximus, could declare at his discretion a short intercalary month to keep the year in step with the seasons. But these pontifices could also abuse their absolute calendar-keeping authority by decreeing the date to be one on which no public business could be done, throwing the calendar out of step. By the first century BCE, the calendar trailed the solar year by more than 67 days!

When Julius Caesar was elected pontifex maximus--about the same time he was declared dictator for life in 45 BCE--he had less need for calendar trickery and was open to major calendar reforms. He changed the lengths of most months to alternate between 30 and 31 days, kept February at 28 days, and so established the familiar year of 365 days. From his time in Egypt (remember Cleopatra?), he knew that astronomers there had observed the solar year to be 365 ¼ days. So, to make up for the day lost every four years, he established that a day would be added to February every fourth year, which would be later known as 'leap year.'

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Additional Info

Introduction

When we modern people study the Roman calendar, we may find its arrangement of days to be absurd. But we can definitely find familiar elements, such as the names of the months. In this lesson, we'll trace the characteristics and history of the Roman calendar, going through its designations for the days, weeks, and months.

Counting the Days

The earliest Roman calendar was based on cycles of the moon, which influenced their method for designating days in a month. The Romans counted down the days to one of three special days: the kalends, nones, and ides. The kalends were the first of the month, coinciding with the new moon; the nones were at the first quarter, and the ides were at the full moon. Later, when the months were disassociated from the lunar cycles, these days were fixed: the kalends on the first of the month, the nones usually on the fifth, and the ides usually on the thirteenth.

Each day in the month was described one of two ways: either as on one of these days ('on the nones of April' was April 5), or by counting down inclusively to the next special day. For example, April 3 was 'three days before the nones of April' (count April 5, April 4, April 3). After the ides had passed, the countdown looked forward to the kalends of the next month: April 14 was, for a Roman, 18 days before the kalends of May.

Days in a Week

Within the month, the Romans used an eight day week that ended in a market day, nunidia. Later, this arrangement lost popularity to the present seven day week.

Above, on this fragmentary Roman calendar, the letters on the left count to the nunidia (H). The numerals count down to the kalends of the next month. The abbreviations on the right show the nunidia (N) and what government business can be done on each day; the smaller text indicates festivals.
ancient Roman calendar

Of Moons and Months

Earliest Roman calendars had ten lunar months, starting with Martius (March), which was the start of the campaigning season and thus sacred to Mars, the Roman war god. Origins for the names of April, May, and June are now unclear. Names for other months came from Latin numbers; for example, decem, 'ten,' provided the name for December, the tenth month of this calendar. About sixty days of winter were left without any designation.

At an early period the Romans formed two months from these nondescript days in winter: January, which was holy to Janus, the god of entrances, and February, which took its name from the Latin verb for purification and atonement. The lunar cycle was dropped, and most months alternated between 29 or 31 days; because of its gloomy associations, February was set at 28 days, providing a year of 355 days.

In the second century BCE, the Romans moved the start of the year to January, so that the magistrates, who assumed office at the year's beginning, could get to far-flung armies before the start of the campaigning season.

Measuring the Year

Even the earliest Romans knew that the solar year was longer than 355 days, so the the chief priest of Rome and keeper the official calendar, the pontifex maximus, could declare at his discretion a short intercalary month to keep the year in step with the seasons. But these pontifices could also abuse their absolute calendar-keeping authority by decreeing the date to be one on which no public business could be done, throwing the calendar out of step. By the first century BCE, the calendar trailed the solar year by more than 67 days!

When Julius Caesar was elected pontifex maximus--about the same time he was declared dictator for life in 45 BCE--he had less need for calendar trickery and was open to major calendar reforms. He changed the lengths of most months to alternate between 30 and 31 days, kept February at 28 days, and so established the familiar year of 365 days. From his time in Egypt (remember Cleopatra?), he knew that astronomers there had observed the solar year to be 365 ¼ days. So, to make up for the day lost every four years, he established that a day would be added to February every fourth year, which would be later known as 'leap year.'

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Frequently Asked Questions

When did Roman calendar start?

The Roman Calendar started in the month of March. However, it didn't just start on "March 1st." The Roman Calendar started on the first signs of the new crescent moon of March, or the Kalends of March.

What month did the Roman calendar start with?

The Roman calendar started with the month of March. The kalends of March or the first sign of the first new crescent moon of March marked the beginning of the year.

Was there a Roman calendar?

Yes, there was a Roman calendar. The Roman calendar is largely what eventually evolved into the modern day calendar. Some of the names of the months in the Roman calendar would look familiar still today.

Who added two months to the calendar?

Likely, Romulus added two months to the calendar. Though this isn't entirely known for sure. But, early historical writing from Roman time periods speak of Romulus adding January and February.

How many days are in a Roman year?

The amount of days in a Roman year has varied throughout history. Sometimes there were only 304 days in a year, other times 355 days a year. However, after the death of Augustus, the Roman calendar contained 365 days a year like the modern calendar. Plus a leap year every four years.

How many months did the Roman calendar have?

The amount of months in the Roman calendar has varied throughout history. For example, under king Romulus there was a period with only 10 months. However, eventually January and February were added, and there became 12 months.

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