Ancient Roman Calendars

Fasti Antiates Maiores - Painting of the Roman calendar about 60 BC, before the Julian reform. Observe (enlarged) that it contains the months Quintilis ("QVI") and Sextilis ("SEX"), and displays the intercalary month ("INTER") as the far righthand column.

The Roman calendar changed its form several times in the time between the foundation of Rome and the fall of the Roman Empire. This article generally discusses the early Roman or 'pre-Julian' calendars. The calendar used after 46 BC is discussed under the Julian calendar.

In order to keep the calendar year roughly aligned with the solar year, a leap month of 27 days, the Mensis Intercalaris, sometimes also known as Mercedonius or Mercedinus, was added from time to time at the end of February, which was shortened to 23 or 24 days. The resulting year was either 377 or 378 days long.

The decision to insert the intercalary month, and its placement, was the responsibility of the pontifex maximus. On average, this happened roughly in alternate years.The system of aligning the year through intercalary months broke down at least twice.

The first time was during and after the Second Punic War. It led to the reform of the Lex Acilia in 191 BC. The details of this reform are unclear, but it appears to have successfully regulated intercalation for over a century.

The second breakdown was in the middle of the first century BC. This breakdown may have been related to the increasingly chaotic and adversarial nature of Roman politics at the time. The position of pontifex maximus was not a full-time job; it was held by a member of the Roman elite, who would almost invariably be involved in the machinations of Roman politics.

Because a Roman calendar year defined the term of office of elected Roman magistrates, a pontifex maximus would have reason to lengthen a year in which he or his allies were in power, or to not lengthen a year in which his political opponents held office.

It was only after Julius Caesar, who had been pontifex maximus for some years, seized absolute power that the calendar was overhauled, with the result being the Julian calendar.

Days of the Week

The Roman Republic, like the Etruscans, used a "market week" of eight days, marked as A to H in the calendar. A market was held on the eighth day. For the Romans, who counted inclusively, this was every ninth day, hence the market became called "nundinae".

Since the length of the year was not a multiple of 8 days, the letter for the market day (known as a "nundinal letter") changed every year. For example, if the current letter for market days was A and the year was 355 days long, then the letter for the next year would be F.

The market cycle was a fundamental rhythm of daily life, and the market day was the day that country people would come to the city.

For this reason, a law was passed in 287 BC (the Lex Hortensia) that forbade the holding of meetings of the comitia (for example to hold elections) on market days, but permitted the holding of legal actions. In the late republic, a superstition arose that it was unlucky to start the year with a market day (i.e. for the market day to fall on 1 January, with a letter A), and the pontiffs, who regulated the calendar, took steps to avoid it.

Because the market cycle was absolutely fixed at 8 days under the Republic, information about the dates of market days is one of the most important tools we have for working out the Julian equivalent of a Roman date in the pre-Julian calendar.

In the early Empire, the Roman market day was occasionally changed. The details of this are not clear, but one likely explanation is that it would be moved by one day if it fell on the same day as the festival of Regifugium, an event that could occur every other Julian leap year. When this happened the market day would be moved to the next day, which was the bissextile (leap) day.

The modern seven-day week came into use during the early imperial period, after the Julian calendar came into effect, apparently stimulated by immigration from the Roman East. For a while it coexisted alongside the old 8-day nundinal cycle, and fasti are known which show both cycles. It was finally given official status by Constantine in 321.

The days of the week were dedicated to the seven planets. They were (note the similarities of some of the days with French and Spanish and other Romance languages):

Character of the Day - An aspect of the Roman calendar that is quite unfamiliar to us is that each day had a "character", which was marked in the fasti. The most important of these were dies fasti, marked by an F, on which legal matters could normally be heard, dies nefasti, marked by an N, on which they could not, and dies comitiales, marked by a C, on which meetings of the public assemblies known as 'comitia' were permitted, subject to other constraints such as the 'Lex Hortensia.' A few days had a different character, e.g. EN ('endotercissus' or perhaps 'endoitio exitio nefas'), a day in which legal actions were permitted on half of the day only, and NP, which were public holidays.

Converting Pre-Julian Dates

Finding the Julian equivalent of a Roman date can be quite tricky. Even early Julian dates, before the leap year cycle was stabilized, are not quite what they appear to be. For example, it is well known that Julius Caesar was assassinated on the Ides of March in 44 BC, and this is usually converted to 15 March 44 BC.

While he was indeed assassinated on the 15th day of the Roman month Martius, the equivalent date on the modern Julian calendar is probably 14 March 44 BC.

Finding the exact Julian equivalent of a pre-Julian date is much harder. Since we have an essentially complete list of the consuls, it is not difficult to find the Julian year that generally corresponds to a pre-Julian year. However, our sources very rarely tell us which years were regular, which were intercalary, and how long an intercalary year was. For this reason, pre-Julian dates can be very misleading.

We do have a number of clues to help us. First, we know when the Julian calendar began, although there is some argument about it. We have detailed sources for the previous decade or so, mostly in the letters and speeches of Cicero. Combining these with what we know about how the calendar worked, especially the nundinal cycle, we can accurately convert Roman dates after 58 BC. Also, the histories of Livy give us exact Roman dates for two eclipses in 190 BC and 168 BC, and we have a few loose synchronisms to dates in other calendars which help to give rough (and sometimes exact) solutions for the intervening period.

Before 190 BC the alignment between the Roman and Julian years is determined by clues such as the dates of harvests mentioned in the sources. This allows us to estimate approximate Julian equivalents of Roman dates back to the start of the First Punic War in 264 BC. However, the number of years before 45 BC for which we can accurately and precisely convert Roman dates to Julian dates is very small.

The Julian Calendar

The Julian calendar was introduced in 46 BC by Julius Caesar and took force in 45 BC (709 ab urbe condita). It was chosen after consultation with the Alexandrian astronomer Sosigenes and was probably designed to approximate the tropical year, known at least since Hipparchus. It has a regular year of 365 days divided into 12 months, and a leap day is added to February every four years.

Hence the Julian year is on average 365.25 days long.The Julian calendar remained in use into the 20th century in some countries and is still used by many national Orthodox churches. However, too many leap days are added with respect to the astronomical seasons on this scheme.

On average, the astronomical solstices and the equinoxes advance by about 11 minutes per year against the Julian year, causing the calendar to gain a day about every 134 years. While Hipparchus and presumably Sosigenes were aware of the discrepancy, although not of its correct value, it was evidently felt to be of little importance.

However, it accumulated significantly over time, and eventually led to the reform of 1582, which replaced the Julian calendar with the more accurate Gregorian calendar.

The notation "Old Style" (OS) is sometimes used to indicate a date in the Julian calendar, as opposed to "New Style", which indicates a date in the Gregorian Calendar. This notation is used when there might otherwise be confusion about which date is found in a text.

The ordinary year in the previous Roman calendar consisted of 12 months, for a total of 355 days. In addition, a 27-day intercalary month, the Mensis Intercalaris, was sometimes inserted between February and March. This intercalary month was formed by inserting 22 days after the first 23 or 24 days of February, the last five days of February becoming the last five days of Intercalaris. The net effect was to add 22 or 23 days to the year, forming an intercalary year of 377 or 378 days.

According to the later writers Censorinus and Macrobius, the ideal intercalary cycle consisted of ordinary years of 355 days alternating with intercalary years, alternately 377 and 378 days long. On this system, the average Roman year would have had 366 1/4 days over four years, giving it an average drift of one day per year relative to any solstice or equinox. Macrobius describes a further refinement wherein, for 8 years out of 24, there were only three intercalary years, each of 377 days. This refinement averages the length of the year to 365 1/4 days over 24 years. In practice, intercalations did not occur schematically according to these ideal systems, but were determined by the pontifices. So far as can be determined from the historical evidence, they were much less regular than these ideal schemes suggest. They usually occurred every second or third year, but were sometimes omitted for much longer, and occasionally occurred in two consecutive years.

If managed correctly this system allowed the Roman year, on average, to stay roughly aligned to a tropical year. However, if too many intercalations were omitted, as happened after the Second Punic War and during the Civil Wars, the calendar would drift rapidly out of alignment with the tropical year. Moreover, since intercalations were often determined quite late, the average Roman citizen often did not know the date, particularly if he were some distance from the city. For these reasons, the last years of the pre-Julian calendar were later known as "years of confusion". The problems became particularly acute during the years of Julius Caesar's pontificate before the reform, 63 to 46 BC, when there were only five intercalary months, whereas there should have been eight, and none at all during the five Roman years before 46 BC.

The reform was intended to correct this problem permanently, by creating a calendar that remained aligned to the sun without any human intervention.

Leap Years

Despite the new calendar being much simpler than the Roman calendar, the pontifices apparently misunderstood the algorithm. They added a leap day every three years, instead of every four years. According to Macrobius, the error was the result of counting inclusively, so that the four year cycle was considered as including both the first and fourth years.

This resulted in too many leap days. Caesar Augustus remedied this discrepancy by restoring the correct frequency after 36 years of this mistake. He also skipped several leap days in order to realign the year.

The historic sequence of leap years (i.e. years with a leap day) in this period is not given explicitly by any ancient source, although the existence of the triennial leap year cycle is confirmed by an inscription that dates from 9 or 8 BC.

The chronologist Joseph Scaliger established in 1583 that the Augustan reform was instituted in 8 BC, and inferred that the sequence of leap years was 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12, 9 BC, AD 8, 12 etc.

This proposal is still the most widely accepted solution. It has also sometimes been suggested that 45 BC was a leap year.

Other solutions have been proposed from time to time. Kepler proposed in 1614 that the correct sequence of leap years was 43, 40, 37, 34, 31, 28, 25, 22, 19, 16, 13, 10 BC, AD 8, 12 etc.

In 1883 the German chronologist Matzat proposed 44, 41, 38, 35, 32, 29, 26, 23, 20, 17, 14, 11 BC, AD 4, 8, 12 etc., based on a passage in Dio Cassius that mentions a leap day in 41 BC that was said to be contrary to (Caesar's) rule.

In the 1960s Radke argued the reform was actually instituted when Augustus became pontifex maximus in 12 BC, suggesting the sequence 45, 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12 BC, AD 4, 8, 12 etc.

In 1999, an Egyptian papyrus was published which gives an ephemeris table for 24 BC with both Roman and Egyptian dates.

From this it can be shown that the most likely sequence was in fact 44, 41, 38, 35, 32, 29, 26, 23, 20, 17, 14, 11, 8 BC, AD 4, 8, 12 etc, very close to that proposed by Matzat.

This sequence shows that the standard Julian leap year sequence began in AD 4, the twelfth year of the Augustan reform.

Also, under this sequence the actual Roman year coincided with the proleptic Julian year between 32 and 26 BC.

This suggests that one aim of the realignment portion of the Augustan reform was to ensure that key dates of his career, notably the fall of Alexandria on 1 August 30 BC, were unaffected by his correction.

Roman dates before 32 BC were typically a day or two before the day with the same Julian date, so 1 January in the Roman calendar of the first year of the Julian reform actually fell on 31 December 46 BC (Julian date).

A curious effect of this is that Caesar's assassination on the Ides (15th day) of March in 44 BC fell on 14 March 44 BC in the Julian calendar.

Naming of the Months

Immediately after the Julian reform, the twelve months of the Roman calendar were named Ianuarius, Februarius, Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, and December, just as they were before the reform.

Their lengths were set to their modern values. The old intercalary month, the Mensis Intercalaris, was abolished and replaced with an single intercalary day at the same point (i.e. five days before the end of Februarius).

The first month of the year continued to be Ianuarius, as it had been since 153 BC.

The Romans later renamed months after Caesar and Augustus, renaming Quintilis (originally, "the Fifth month", with March = month 1) as Iulius (July) in 44 BC and Sextilis ("Sixth month") as Augustus (August) in 8 BC.

(Note that the letter J was not invented until the 17th century).

Quintilis was renamed to honour Caesar because it was the month of his birth. According to a senatusconsultum quoted by Macrobius, Sextilis was renamed to honour Augustus because several of the most significant events in his rise to power, culminating in the fall of Alexandria, fell in that month.

Other months were renamed by other emperors, but apparently none of the later changes survived their deaths.

Caligula renamed September ("Seventh month") as Germanicus; Nero renamed Aprilis (April) as Neroneus, Maius (May) as Claudius and Iunius (June) as Germanicus; and Domitian renamed September as Germanicus and October ("Eighth month") as Domitianus.

At other times, September was also renamed as Antoninus and Tacitus, and November ("Ninth month") was renamed Faustina and Romanus. Commodus was unique in renaming all twelve months after his own adopted names (January to December): Amazonius, Invictus, Felix, Pius, Lucius, Aelius, Aurelius, Commodus, Augustus, Herculeus, Romanus, and Exsuperatorius.

Much more lasting than the ephemeral month names of the post-Augustan Roman emperors were the names introduced by Charlemagne.

He renamed all of the months agriculturally into Old High German.

They were used until the 15th century, and with some modifications until the late 18th century in Germany and in the Netherlands (January-December): Wintarmanoth (winter month), Hornung (spring), Lentzinmanoth (Lent month), Ostarmanoth (Easter month), Winnemanoth (grazing month), Brachmanoth (plowing month), Heuvimanoth (hay month), Aranmanoth (harvest month), Witumanoth (wood month), Windumemanoth (vintage month), Herbistmanoth (autumn/harvest month), and Heilagmanoth (holy month). Translations of these month names are still used to this day in some Slavic languages, such as Polish.

Year Numbering

The dominant method that the Romans used to identify a year for dating purposes was to name it after the two consuls who took office in it. Since 153 BC, they had taken office on 1 January, and Julius Caesar did not change the beginning of the year. Thus this consular year was an eponymous or named year. Roman years were named this way until the last consul was appointed in 541.

Only rarely did the Romans number the year from the founding of the city (of Rome), ab urbe condita (AUC). This method was used by Roman historians to determine the number of years from one event to another, not to date a year. Different historians had several different dates for the founding.

The Fasti Capitolini, an inscription containing an official list of the consuls which was published by Augustus, used an epoch of 752 BC.

The epoch used by Varro, 753 BC, has been adopted by modern historians. Indeed, Renaissance editors often added it to the manuscripts that they published, giving the false impression that the Romans numbered their years.

Most modern historians tacitly assume that it began on the day the consuls took office, and ancient documents such as the Fasti Capitolini which use other AUC systems do so in the same way. However, the Varronian AUC year did not formally begin on 1 January, but on Founder's Day, 21 April.

This prevented the early Roman church from celebrating Easter after 21 April because the festivities associated with Founder's Day conflicted with the solemnity of Lent, which was observed until the Saturday before Easter Sunday.

In addition to consular years, the Romans sometimes used the regnal year of the emperor. Anno Diocletiani, named after Diocletian, was often used by the Alexandrian Christians to number their Easters during the fourth and fifth centuries.

In AD 537, Justinian required that henceforth the date must include the name of the emperor, in addition to the indiction and the consul (the latter ending only four years later). The indiction caused the Byzantine year to begin on 1 September, which is still used in the Eastern Orthodox Church for the beginning of the liturgical year.

In AD 525 Dionysius Exiguus proposed the system of anno Domini, which gradually spread through the western Christian world, once the system was adopted by Bede.

Years were numbered from the supposed date of the incarnation or annunciation of Jesus on 25 March, although this soon changed to Christmas, then back to Annunciation Day in Britain, and the numbered year even began on Easter in France.

From Julian to Gregorian

The Julian calendar was in general use in Europe from the times of the Roman Empire until 1582, when Pope Gregory XIII promulgated the Gregorian Calendar, which was soon adopted by most Catholic countries.

The Protestant countries followed later, and the countries of Eastern Europe even later. Great Britain had Thursday 14 September 1752 follow Wednesday 2 September 1752.

Sweden adopted the new style calendar in 1753, but also for a twelve-year period starting in 1700 used a modified Julian Calendar.

Russia remained on the Julian calendar until after the Russian Revolution (which is thus called the 'October Revolution' but occurred in November according to the Gregorian calendar), in 1917, while Greece continued to use it until 1923.

Although all Eastern European countries had adopted the Gregorian calendar on or before 1923, their national Eastern Orthodox churches had not.

A revised Julian calendar was proposed during a synod in Constantinople in May of 1923, consisting of a solar part which was and will be identical to the Gregorian calendar until the year 2800, and a lunar part which calculated Easter astronomically at Jerusalem.

All Orthodox churches refused to accept the lunar part, so almost all Orthodox churches continue to celebrate Easter according to the Julian calendar (the Finnish Orthodox Church uses the Gregorian Easter).

The solar part was only accepted by some Orthodox churches, those of Constantinople, Alexandria, Antioch, Greece, Cyprus, Romania, Poland, Bulgaria (in 1963), and the Orthodox Church in America (although some OCA parishes are permitted to use the Julian calendar).

Thus, these churches celebrate the Nativity on the same day that Western Christians do, 25 December Gregorian until 2800. The Orthodox churches of Jerusalem, Russia, Serbia, Georgia, Ukraine, and the Greek Old Calendarists continue to use the Julian calendar for their fixed dates, thus they celebrate the Nativity on 25 December Julian (7 January Gregorian until 2100).

Lengths of the Months

According to the 13th century scholar Sacrobosco, the original scheme for the months in the Julian Calendar was very regular, alternately long and short. From January through December, the month lengths according to Sacrobosco for the Roman Republican calendar were:

He then thought that Julius Caesar added one day to every month except February, a total of 11 more days, giving the year 365 days. A leap day could now be added to the extra short February:

He then said Augustus changed this to:

giving us the irregular month lengths which we still use today, so that the length of Augustus would not be shorter than (and therefore inferior to) the length of Iulius.

Although this theory is still widely repeated, it is certainly wrong. First, a wall painting of a Roman Republican calendar has survived which confirms the literary accounts that the months were already irregular before Julius Caesar reformed it:

Also, the Julian reform did not change the dates of the Nones and Ides. In particular, the Ides are late (on the 15th rather than 13th) in March, May, July and October, showing that these months always had 31 days in the Roman calendar, whereas Sacrobosco's theory requires that the length of October was changed.

Further, Sacrobosco's theory is explicitly contradicted by the third and fifth century authors Censorinus and Macrobius, and, finally, it is inconsistent with seasonal lengths given by Varro, writing in 37 BC, before the Augustan reform, with the 31-day Sextilis given by the new Egyptian papyrus from 24 BC, and with the 28-day February shown in the Fasti Caeretani, which is dated before 12 BC.

Origins of the Names of the Months

January - Janus, Roman god of doors, beginnings, sunset and sunrise, had one face looking forward and one backward,

February - On February 15 the Romans celebrated the festival of forgiveness for sins; (februare, Latin to purify)

March - Mars, the Roman god of war

April Roman month Aprilis, perhaps derived from aperire, (Latin to open, as in opening buds and blossoms) or perhaps from Aphrodite, original Greek name of Venus,

May Maia, Roman goddess, mother of Mercury by Jupiter and daughter of Atlas,

June - Juno, chief Roman goddess

July - Renamed for Julius Caesar in 44 BC, who was born this month; Quintilis, Latin for fifth month, was the former name (The Roman year began in March rather than January),

August - Formerly Sextilis (sixth month in the Roman calendar); re-named in 8 BC for Augustus Caesar,

September - September, (septem, Latin for 7) the seventh month in the Julian or Roman calendar, established in the reign of Julius Caesar,

October - Eighth month (octo, Latin for 8) in the Julian (Roman) calendar. The Gregorian calendar instituted by Pope Gregory XIII established January as the first month of the year,

November - Ninth Roman month (novem, Latin for 9). Catholic countries adopted the Gregorian calendar in 1582, skipping 10 days that October, correcting for too many leap years,

December - Julian (Roman) year's tenth month (decem, Latin for 10).