The Roman Calendar

Here, we focus mainly on the calendar used in the Roman Republic (509-27 BCE). Also known as the Republican calendar, it is the earliest calendar system from Rome for which we have historical evidence. It was used until 45 BCE, when it was replaced by the Julian calendar.

Some calendars were carved in marble or stone, but many were painted on walls for decoration.

The Calendar of Romulus

The Republican calendar was derived from a line of older calendar systems whose exact design is largely unknown. It is believed that the original Roman calendar was a lunar calendar that followed the phases of the Moon. This basic structure was preserved through the centuries, which is the reason why we use months today.

Only 10 Months at First

The Romans borrowed parts of their earliest known calendar from the Greeks. According to tradition, Romulus, the legendary first king of Rome, oversaw an overhaul of the Roman calendar system around 738 BCE. The resulting calendar, had only 10 months, beginning with March (Martius) in the spring and ending in December with the autumn planting, the year then was ten months long and had six months of thirty days and four of thirty-one, for a total of 304 days.

The 10 months were named Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December – with the last six names were taken from the words for five, six, seven, eight, nine, and ten. The winter season was not assigned to any month, so the year only lasted 304 days, with 61 days unaccounted for in the winter.

The Calendar of Numa

Following another calendar reform, which later Roman writers attributed to Romulus’ successor, Numa Pompilius, the second of the seven traditional Kings of Rome, the Republican calendar was instituted. To account for the days of winter between the years, two additional months were introduced: Ianuarius (January) and Februarius (February).

And first of all he [Numa Pompilius] divided the year into twelve months, according to the revolutions of the moon. But since the moon does not give months of quite thirty days each, and eleven days are wanting to the full complement of a year as marked by the sun’s revolution, he inserted intercalary months in such a way that in the twentieth year the days should fall in with the same position of the sun from which they had started, and the period of twenty years be rounded out. 

Titus Livius (Livy), The History of Rome, Book 1, Chapter 19

This meant that some of the month names no longer agreed with their position in the calendar. For example, September means “the 7th month,” but it was now the 9th month of the year—an inconsistency that was preserved and is still part of the Gregorian calendar we use today.

A common year was now divided into 12 months of different lengths: 4 “full” months with 31 days, 7 “hollow” months with 29 days, and 1 month with 28 days.

The Leap Month, Mercedonius

The Republican calendar year lasted for 355 days, which is about 10 days shorter than a tropical year, the time it takes Earth to revolve around the Sun. To keep the calendar in sync with the seasons, a leap month called Mercedonius or Intercalaris was added in some years—normally every two to three years.

By custom, the insertion of the leap month was initiated by the pontifex maximus, the high priest of the College of Pontiffs in ancient Rome. However, this system was vulnerable to abuse. Since the Roman calendar year defined the term of office of elected officials, a pontifex maximus was able to control the length of his term simply by adding a leap month.

When Julius Caesar became pontifex maximus, he ordered a calendar reform which eliminated leap months and resulted in the implementation of the Julian calendar in 45 BCE, the direct predecessor of today’s Gregorian calendar.

The Julian Calendar

While Caesar was in Alexandria, Egypt, he had access to the ancient world’s foremost astronomy experts. The Egyptians were able to calculate the length of the actual solar year as 365.25 days and the winter solstice as December 24.

In 45 B.C.E., Romans modified their method of marking time to keep it in phase with seasons, but not require intercalation of an extra month. They accomplished this with the Julian Calendar. Month lengths were extended to bring the calendar’s total to 365 days, making it truly solar. This change was accompanied by addition of an extra day every fourth year (after February 23rd) because of the almost six extra hours beyond 365 days in a tropical year.

The new Julian Calendar would follow the solar year, rather than lunar, with a total of 365 days vs. 355. The intercalary month was eliminated and the leap year, adding a day to February every 4th year, was adopted as well. In 46 BC, the calendar had to be set right before the new one could begin. A total of 3 intercalary months were inserted prior to the start of the new year. 46 BC, therefore, or 707 AUC to the Romans, was fifteen months and about 445 days long according to the calendar.

Inasmuch as the calendar, which had been set in order by the Deified Julius, had later been confused and disordered through negligence, he restored it to its former system;​d and in making this arrangement he called the month Sextilis by his own surname, rather than his birth-month September, because in the former he had won his first consul­ship and his most brilliant victories.

Suetonius, The Lives of the Caesars, The Life of Augustus, Chapter 31

The fifth month, Quintilis, was renamed Julius (July) in honor of Julius Caesar. Likewise, Sextilis was changed in 8 BC in honor of his heir and eventual first Emperor, Augustus, changing it to the name we now know as August. This basic transformation has essentially remained intact for two millennia and represents the foundation of the western calendar still in use today.

Months of the Year

Mensis = MonthOrigin of Name
Januarius = JanuaryGod Janus
Februarius = FebruaryFebrua Festivals
Martius = MarchWar God Mars
Aprilis = AprilGoddess Aprilis of the Etruscans
Maius = MayEarth Goddess Maia
Junius = JuneGoddess Juno
Julius = JulyBirth of the Divine Julius Caesar; originally quintillis
Augustus = AugustBirth of the Divine Augustus Caesar; originally sextilis
September‘The Seventh Month’
October‘The Eighth Month’
November‘The Ninth Month’
December‘The Tenth Month’

How did the Roman Refer to Years?

A period of five years was called a “lustrum” on account of the sacrifice performed by the Consuls after the five yearly census of the people. The sacrifice was called the Suovetaurilia, the animals sacrificed by the Romans were a pig, a sheep and a bull and performing it was referred to as “lustrum condere” hence the “lustrum”.

The Romans referred to years in a couple of ways. Each year was recorded as a length of time from the traditional founding of Rome, in 753 BC. The Latin term Ab Urbe Condita, abbreviated as AUC, literally meaning from the founding of the city, was the correct terminology. Additionally, years could be referred to as the year in which a particular Consul was in office. As examples, the modern year 59 BC, would’ve been known as 694 AUC, or the year of the first consulship of Gaius Julius Caesar.

Calends, Nones, and Ides

The Roman calendar highlighted a number of days in each month:

  • Calends (Kalendae) were the first days of each month. The name is derived from the Greek word καλειν, to announce, which may initially have been used in the ancient lunar calendar to “announce” the day of the New Moon (or the first sliver of the Waxing Crescent Moon). It was dedicated to the goddess Juno.
  • Ides (Idus) occurred one day before the middle of each month. Depending on the month’s length, it fell on the 13th or 15th day. In the lunar calendar, the Ides marked the day of the Full Moon.
  • Nones (Nonae) fell on the 7th day of 31-day months and on the 5th day of 29-day months, marking the day of the First Quarter Moon.

These markers were used to number the days in each month, counting backward from the upcoming Calends, Ides, or Nones. The count always included the day of the marker. For example, the 11th day of Martius would be known as “Five Ides” to the Romans because it is the fifth day before the Ides of Martius, which fell on the 15th day.

Days of the Month

At the time of their early kings, Roman months were of a length identical to the lunar cycle. The Romans did not number the days of the months consecutively. They reckoned backwards from three fixed points: The kalends, the nones, and the ides. The kalends is the first day of the month. For monthswith 31 days the nones fall on the 7th and the ides the 15th. All days were referred to in terms of one of these three moon phase names, Kalends, Nones or Ides.

At that time a pontifex (priest) was assigned to observe the sky. When he first sighted a thin lunar crescent he called out that there was a new moon and declared the next month had started. For centuries afterward, Romans referred to the first day of each month as Kalendae or Kalends from the Latin word calare (to announce solemnly, to call out). The word calendar was derived from this custom.

Days of the Week

Macrobius tells us that at first, the Romans used the ancient Etruscan Market Week, which consisted of seven working days followed by a market day called the Nunindae. During this eighth day many public auctions were held, and Varro joked that the rural population shaved and came into the city, thus the Nunindae became a day of festivity.

“The custom, however, of referring the days to the seven stars called planets was instituted by the Egyptians, but is now found among all mankind, though its adoption has been comparatively recent; at any rate the ancient Greeks never understood it, so far as I am aware.” (Cassius Dio, History of Rome, XXXVII, 18.1)

The astrological or planetary week of seven days is thought to have started in Persian theology, and by the end of the first century AD was in common usage throughout the whole Mediterranean world. Although the planetary week was recognised by the emperor Augustus, he continued to run the ancient market calendar alongside, and it was not until 321AD during the rule of emperor Constantine that the astrological week became fully established in Roman law.

Days of the Week

Dies = DayAssociated Deity/Celestial Object
dies Solis ‘Sun day’ = SundayPhoebus, the Sun Apollo.
dies Lunae ‘Moon day’ = MondayLuna, Selene, Delia or Phoebe, Diana the Moon.
dies Martis ‘the day of Mars’ = TuesdayMars, master of Flight and Terror. (compare French Mardi)
dies Mercuris ‘the day of Mercury’ = WednesdayMercury, swift Hermes, Father of Astrology. (compare French Mercredi)
dies Iovis ‘the day of Jupiter’ = ThursdayJupiter or Jove, ruler of all the Gods.
dies Veneris ‘the day of Venus’ = FridayVenus Astarte, both Hesperos and Lucifer. (compare French Vendredi)
dies Saturni ‘the day of Saturn’ = SaturdaySaturn, of the ‘Golden Age’.

The Astrological Week

Roman DayTranslationModern EquivalentModern Derivation
dies Saturni‘the day of Saturn’SaturdayDirectly from Latin.
dies Solis‘Sun day’SundayLikewise.
dies Lunae‘Moon day’MondayDitto.
dies Martis‘the day of Mars’TuesdayOE Tiwesdaeg ‘The day of Tiw’, from Norse Tysdagr.
dies Mercuris‘the day of Mercury’WednesdayOE Wodnesdaeg ‘the day of Woden’, from Norse Odinsdagr.¹
dies Iovis‘the day of Jupiter’ThursdayOE Thursdaeg ‘the day of Thor’, from Norse Thorsdagr.²
dies Veneris‘the day of Venus’FridayOE Frigesdaeg ‘the day of Freya’, from Norse Freyjasdagr.³
  1. Compare Modern Dutch: Woensdag.
  2. Compare Old German: Donares Tag ‘The Thunderer’s Day’; Modern German Donnerstag.
  3. Compare Old High German Friatag, and Old Frisian Friadei.

Roman Time of Day

Like us, the Romans divided each day into 24 hours, and they assigned 12 to the daytime and 12 to the night. These did not run from midnight to midnight as our modern method of timekeeping does, but from sunrise to sunrise. This effectively means that the length of the Roman hour varied according to the season, so that during the summer solstice¹ around June 21st when the period of daylight is considerably longer than the night, the twelve hours assigned to the daytime would each have to be 1 hour and 16 minutes long, while conversely, during the short days of the winter solstice around December 21st, each daylight hour would be only 44 minutes long.

There were only two days during the entire year when the Roman day contained hours of exactly 60 minutes. These dates occurred during the equinoxes,² when the length of the day is exactly equal to that of the night; the vernal equinox occurred every year around March 21st, and the autumnal equinox about September 21st.

This fluid method of timekeeping was perfectly natural to your average Roman, who was not governed by the same rigid schedules prevalent in our modern technological society and carried neither a wristwatch nor an iPad.

  1. From Latin solstitium, from sol ‘sun’ + sistere ‘to stand still’.
  2. From late Latin equinoxium, early Latin aequinoctium, from aequi ‘equal’ + nox ‘night’.

Norse Mythology & Days of the Week

The last four days of the week are named in English after Viking gods, and it behooves our purpose to here present a short summation of the four gods from the Norse pantheon after which our modern day names have been derived. Tiw Or Tiu, was the name of the Anglo-Saxon god of war and the sky. A.k.a. Norse Tyr (son of Odin) or Germanic Tiwaz. This defender-god was also a sage, and was likened by the Romans with Mars, their own god of war. He was an ancestor god of Norse mythology, tradtionally depicted as an old sage dressed in animal skins and bearing a sceptre in his right hand. Odin Alternately spelled Othinn, this god was also known as Woden in Britain and Wotan or Wodan in Germany. He was god of magic, poetry, ecstacy, wealth and the gain of riches, possibly with healing, and also the dead. He was leader of the Aesir, the Norse pantheon, and the Valkyries were his to command; these warrior-maidens conducted the souls of dead heroes to the Halls of Valhalla, over which he held dominion. His most fanatic followers were the Berserkers, who fought ‘bare-sark’, without armour or clothing, believing that their swift death in battle would be rewarded by a place in Valhalla. He appeared as a tall, spear carrying warrior accompanied by a raven, an eagle and a wolf, and riding his eight-legged horse Sleipnir, a magical beast capable of carrying him across the sky. The Romans equated him with Mercury. Important myths associated with Odin were the ‘regaining of the mead of inspiration’, ‘the sacrifice of an eye to gain knowledge’, and ‘the aquisition of runic lore through hanging in torment upon Yggdrasil, the World-Tree, the Guardian Ash of the Aesir. Odin was doomed to be devoured by Fenris Wulf during the battle of Ragnarok, which name in Iclandic means ‘the twilight of the powers’, and signified the end of the Aesir, as both Thor and the treacherous Loki were also killed. Thor His name stems from the Old Norse word for thunder, thorr, equivalent to the German god Donar, Anglo-Saxon Thunor also Taranis. Equivalent with Roman Jupiter¹ or Greek Zeus, a sky-god who controlled the winds and weather, and made thunder sound by hitting the earth with his mighty hammer, which was manifested on earth as the destruction caused by bolts of lightning. He was also attributed with upholding the law of the Aesir, presided over the Law Assembly, and the protection of the community was in his charge. Associated with the oak. Oaths were sworn on his sacred ring. Depicted as a red-bearded waggon driver with a ravenous appetite, who caused thunder to sound as his cart lumbered across the sky. His symbols were the hammer and the swastika. Tales include his encounter with the frost giants and fishing for the world-serpent. He perished in battle with the serpent during Ragnarok, the final battle of the Aesir. Freya One of the Vanir, the Scandinavian fertility deities, linked with spirits of the land and with dead ancestors. She was the goddess of love and fecundity, and the sister of Freyr, the god of male fertility. Their father was Njord, patron god of ships, and god of all the seas and lakes. Her image was loaded on a wagon and carted from farmhouse to steading, to ensure a fruitful season’s harvest. She has been identified with Odin’s wife, Frigg, also with the Germanic goddess Frija, her Roman equivalent was Venus and in Greek mythology, Aphrodite. Her associated symbols were a ship and a golden boar.