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The Roman Calendar

The ancient Roman calendar, or “pre-Julian” calendar, is believed to have been a lunar calendar. The calendar originally consisted of hollow months that were 29 days long or full months that had 30 days.

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The Colosseum in Rome.

The Colosseum in Rome is one of the most famous ruins from the Roman era.

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King Romulus

The original Roman calendar was said to be invented by Romulus, the first king of Rome, around 753 BCE. The calendar started the year in March (Martius) and consisted of 10 months, with 6 months of 30 days and 4 months of 31 days. The winter season was not assigned to any month, so the calendar year only lasted 304 days with 61 days unaccounted for in the winter.

Calendar of Romulus:

  1. Martius - 31 Days
  2. Aprilis - 30 Days
  3. Maius - 31 Days
  4. Iunius - 30 Days
  5. Quintilis - 31 Days
  6. Sextilis - 30 Days
  7. September - 30 Days
  8. October - 31 Days
  9. November - 30 Days
  10. December - 30 Days

Calends, Nones, and Ides

Unlike the Julian and Gregorian calendars, the Roman calendar had a different system for numbering the days of the month. The months were divided into day markers that fell at the start of the month, the fifth or seventh day, and in the middle of the month. These 3 markers were called Calends, Nones and Ides.

Calends (Kalendae, Kalends) signify the start of the new moon cycle and the first day of the month. The name is derived from the Greek word καλειν, “to announce” the days of the full and new moon.

Nones (Nonae) were known to be the days of the half moon which usually occur 8 days before the Ides.

Ides occurred on the 15th day of March, May, July, and October, and the 13th day of the other months. They are thought to have been the days of the full moon.

Each day was referred to by how many days it fell before the Calends, Nones or Ides. For example, March 11 would be known as “Five Ides” to the Romans because it is four days before the Ides of March (March 15).

Adding January and February

The 304-day Roman calendar didn’t work for long because it didn’t align with the seasons. King Numa Pompilius reformed the calendar around 700 BCE by shortening the 30-day months to 29 days and adding the 29-day month of January (Ianuarius) and the 28-day month of February (Februarius) to the original 10 months. This increased the year's length to 354 or 355 days.

The addition of January and February meant that some of the months' names no longer agreed with their position in the calendar (September - December). The month Quintilis was renamed July in honor of Julius Caesar in 44 BCE and Sextilis was renamed August in honor of Augustus in 8 BCE.

The Intercalary Month

The Roman calendar was still flawed after adding January and February, as well as the days and months needed to keep the calendar in line with the seasons. Many attempts were made to align the calendar with the seasons but all failed. An extra month was added to the calendar in some years to make up for the lack of days in a year.

The insertion of the intercalary month was made by the pontifex maximus, the high priest of the College of Pontiffs in ancient Rome. However this system was flawed because the Roman calendar year defined the term of office of elected officials, thus a pontifex maximus could control the length of the year depending on their political agenda.

When Julius Caesar became pontifex maximus, he reformed the calendar by getting rid of the intercalary months. The Julian calendar was created, then completed during his successor Augustus' reign.

Roman Calendar Months

Common YearNumber of daysLeap YearNumber of days
Ianuarius29Ianuarius29
Februarius28Februarius23/24
Martius31Intercalaris27/28
Aprilis29Martius31
Maius31Aprilis29
Iunius29Maius31
Quintilis31Iunius29
Sextilis29Quintilis31
September29Sextilis29
October31September29
November29October31
December29November29
  December29

Topics: Calendar, History

The Roman calendar / “Pre-Julian” calendar
Used inThe Roman Empire
Calendar typeLunar or lunisolar
Number of days354 or 355

Number of monthsFirst 10, later 12
Correction mechanismIntercalary month

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Calendar History

  1. Gregorian Calendar
  2. Julian Calendar
  3. Switch from Julian to Gregorian
  4. Roman Calendar
  5. What Do CE and BCE Mean?

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Calendars Worldwide

  1. Hindu Calendar
  2. Buddhist Calendar
  3. Islamic Calendar
  4. Jewish Calendar
  5. Persian Calendar
  6. Chinese Calendar
  7. Coptic Calendar
  8. Ethiopian Calendar
  9. Revised Julian Calendar
  10. Mayan Calendar

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