Julian calendar

The Julian calendar was a reform of the which was introduced by  in  and came into force in  (709 ). It was chosen after consultation with the astronomer and was probably designed to approximate the, known at least since. It has a regular year of 365 s divided into 12 s, and a is added to  every four years. Hence the Julian year is on average 365.25 days long.

The Julian calendar remained in use into the in some countries as a national calendar, but it has generally been replaced by the modern. It is still used by the of  and by many national  churches. Orthodox Churches no longer using the Julian calendar typically use the rather than the Gregorian calendar.

The notation is sometimes used to indicate a date in the Julian calendar, as opposed to, which either represents the Julian date with the start of the year as  or a full mapping onto the.

Motivation
The ordinary year in the previous consisted of 12 months, for a total of 355 days. In addition, a 27-day intercalary month, the, 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 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 366¼ days over four years, giving it an average drift of one day per year relative to any solstice or equinox. 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 365¼ days over 24 years. In practice, intercalations did not occur schematically according to these ideal systems, but were determined by the. 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 and during the, 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, to, 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.

Julian reform
The first step of the reform was to realign the start of the calendar year to the tropical year by making  445 days long, compensating for the intercalations which had been missed during Caesar's pontificate. This year had already been extended from 355 to 378 days by the insertion of a regular in February. When Caesar decreed the reform, probably shortly after his return from the African campaign in late Quintilis (July), he added 67 (=22+23+22) more days by inserting two extraordinary intercalary months between November and December. These months are called "Intercalaris Prior" and "Intercalaris Posterior" in letters of Cicero written at the time; there is no basis for the statement sometimes seen that they were called "Unodecember" and "Duodecember". Their individual lengths are unknown, as is the position of the Nones and the Ides within them. Because was the last of a series of irregular years, this extra-long year was, and is, referred to as the last year of confusion. The first year of operation of the new calendar was 45 BC.

The Julian months were formed by adding ten days to a regular pre-Julian Roman year of 355 days, creating a regular Julian year of 365 days: Two extra days were added to Ianuarius, Sextilis (Augustus) and December, and one extra day was added to Aprilis, Iunius, September and November, setting the lengths of the months to the values they still hold today:

states that the extra days were added immediately before the last day of each month to avoid disturbing the position of the established Roman fasti (days prescribed for certain events) relative to the start of the month. However, since Roman dates after the of the month counted down towards the start of the next month, the extra days had the effect of raising the initial value of the count of the day after the Ides. Romans of the time born after the Ides of a month responded differently to the effect of this change on their birthdays. kept his birthday on the 14th day of Ianuarius, which changed its date from a.d. XVII Kal. Feb. to a.d. XIX Kal. Feb., a date that had previously not existed. kept the date of her birthday unchanged at a.d. III Kal. Feb., which moved it from the 28th to the 30th day of Ianuarius, a day that had previously not existed. kept his on the 23rd day of September, but both the old date (a.d. VIII Kal. Oct.) and the new (a.d. IX Kal. Oct.) were celebrated in some places.

The old was abolished. The new leap day was originally inserted following, a.d. VI Kal. Mar. by Roman reckoning, since this is the point at which intercalary months were inserted in the pre-Julian calendar. It was considered as extending that day to 48 hours, so it was dated as "a.d. VI bis Kal. Mar.", and is called the bissextile day. During the late when days in the month came to be numbered in consecutive day order, the Leap Day was considered to be the last day in February in leap years, i.e..

Leap year error
Although the new calendar was much simpler than the pre-Julian calendar, the pontifices apparently misunderstood the algorithm for leap years. 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. remedied this discrepancy after 36 years by restoring the correct frequency. He also skipped several leap days in order to realign the year.

The historic sequence of leap years 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 or. The  established in  that the Augustan reform was instituted in, 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 sometimes been suggested that there was an additional bissextile day in the first year of the Julian reform, i.e. that was also a leap year.

Other solutions have been proposed from time to time. proposed in 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  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  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, suggesting the sequence 45, 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12 BC, AD 4, 8, 12 etc. With all these solutions, except that of Radke, the Roman calendar was not finally aligned to the Julian calendar of later times until (a.d. V Kal. Mar.). On Radke's solution, the two calendars were aligned on.

In 1999, an Egyptian was published that gives an  table for  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, the 12th year of the Augustan reform, and that the Roman calendar was finally aligned to the Julian calendar in , as in Radke's model. The Roman year also 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, 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 in the Roman calendar of the first year of the Julian reform was   (Julian date). A curious effect of this is that Caesar's assassination on the Ides (15th day) of March fell on  in the Julian calendar.

Month names
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. The old intercalary month, the, was abolished and replaced with a 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.

The Romans later renamed months after and, 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. Quintilis was renamed to honour Caesar because it was the month of his birth. According to a senatus consultum 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. renamed September ("Seventh month") as ; renamed Aprilis (April) as Neroneus, Maius (May) as Claudius and Iunius (June) as Germanicus; and  renamed September as  and October ("Eighth month") as Domitianus. At other times, September was also renamed as and, and November ("Ninth month") was renamed as  and Romanus. 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. He renamed all of the months agriculturally into. They were used until the, and with some modifications until the late in Germany and in the Netherlands (January-December): Wintarmanoth (winter month), Hornung (the month when the male red deer sheds its antlers), Lentzinmanoth (Lent month), Ostarmanoth (Easter month), Wonnemanoth (love making month), Brachmanoth (plowing month), Heuvimanoth (hay month), Aranmanoth (harvest month), Witumanoth (wood month), Windumemanoth (vintage month), Herbistmanoth (autumn/harvest month), and Heilagmanoth (holy month).

Month lengths
The Julian reform set the lengths of the months to their modern values. However, a 13th century scholar,, proposed a different explanation for the lengths of Julian months which is still widely repeated but is certainly wrong. According to 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:

30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29

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:

31, 29/30, 31, 30, 31, 30, 31, 30, 31, 30, 31, 30

He then said Augustus changed this to:

31, 28/29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31

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

There is abundant evidence disproving this theory. First, a wall painting of a predating the Julian reform has survived, which confirms the literary accounts that the months were already irregular before Julius Caesar reformed them:

29, 28, 31, 29, 31, 29, 31, 29, 29, 31, 29, 29

Also, the Julian reform did not change the dates of the and. In particular, the Ides were 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 March, May and July were originally 30 days long and that the length of October was changed from 29 to 30 days by Caesar and to 31 days by Augustus. Further, Sacrobosco's theory is explicitly contradicted by the third and fifth century authors and, and it is inconsistent with seasonal lengths given by Varro, writing in , before the Augustan reform, with the 31-day Sextilis given by the new Egyptian papyrus from , and with the 28-day February shown in the Fasti Caeretani, which is dated before.

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, they had taken office on , and Julius Caesar did not change the beginning of the year. Thus this consular year was an eponymous or named year. In addition to consular years, the Romans sometimes used the regnal year of the emperor, and by the late fourth century documents were also being dated according to the 15-year cycle of the. In, required that henceforth the date must include the name of the emperor and his regnal year, in addition to the  and the consul, while also allowing the use of local eras.

In and, and from time to time thereafter, no consuls were appointed. When this happened, the consular date was given a count of years since the last consul (so-called "post-consular" dating). After, only the reigning emperor held the consulate, typically for only one year in his reign, and so post-consular dating became the norm. Similar post-consular dates are also known in the West in the early sixth century. The last known post-consular date is year 22 after the consulate of. The last emperor to hold the consulate was. The system of consular dating, long obsolete, was formally abolished in the law code of, issued in 888.

Only rarely did the Romans number the year from the,  (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, an inscription containing an official list of the consuls which was published by Augustus, used an of. The epoch used by, , has been adopted by modern historians. Indeed, 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,, writing in the third century AD, states that, in his time, the AUC year began with the , celebrated on , which was regarded as the actual anniversary of the foundation of Rome. Because the festivities associated with the Parilia conflicted with the solemnity of, which was observed until the Saturday before Easter Sunday, the early Roman church did not celebrate Easter after.

While the Julian reform applied originally to the Roman calendar, many of the other calendars then used in the Roman Empire were aligned with the reformed calendar under. This led to the adoption of several local eras for the Julian calendar, such as the and the, some of which were used for a considerable time. Perhaps the best known is the, sometimes also called Anno Diocletiani (after ), which was often used by the to number their Easters during the  and  and continued to be used by the Coptic and Abyssinian churches.

In the Eastern Mediterranean, the efforts of Christian chronographers such as to date the Biblical creation of the world led to the introduction of  eras based on this event. The most important of these was the, used throughout the Byzantine world from the 10th century and in Russia till 1700. In the West,  proposed the system of  in. This era gradually spread through the western Christian world, once the system was adopted by.

New Year's Day
The Roman calendar began the year on, and this remained the start of the year after the Julian reform. However, even after local calendars were aligned to the Julian calendar, they started the new year on different dates. The in Egypt started on  ( after an Alexandrian leap year). Several local provincial calendars were aligned to start on the birthday of Augustus,. The caused the  year, which used the Julian calendar, to begin on ; this date is still used in the  for the beginning of the. When the Julian calendar was adopted in Russia in AD 988 by, the year was numbered 6496, beginning on , six months after the start of the Byzantine Anno Mundi year with the same number. In 1492 (AM 7000),, according to church tradition, realigned the start of the year to , so that AM 7000 only lasted for six months in Russia, from to  1492.

During the  retained the name  (or an equivalent name) in all an countries (affiliated with the ), since the medieval calendar continued to display the months from January to December (in twelve columns containing 28 to 31 days each), just as the Romans had. However, most of those countries began their numbered year on (the Nativity of ),  (the ), or even, as in  (see the  article for more details).

In England before 1752, was celebrated as the New Year festival, but the "year starting 25th March was called the Civil or Legal Year, although the phrase  was more commonly used." To reduce misunderstandings on the date, it was not uncommon in parish registers for a new year heading after for example 1661 had another heading at the end of the following December indicating "1661/62". This was to explain to the reader that the year was 1661 Old Style and 1662 New Style.

Most Western European countries shifted the first day of their numbered year to while they were still using the Julian calendar, before they adopted the Gregorian calendar, many during the. The following table shows the years in which various countries adopted as the start of the year. Eastern European countries, with populations showing allegiance to the, began the year on from about.

Note that as a consequence of change of New Year, 1 January 1751 to 24 March 1751 were non-existent dates in England.

From Julian to Gregorian
The Julian calendar was in general use in Europe and Northern Africa from the times of the until 1582, when  promulgated the. Reform was required because too many leap days are added with respect to the astronomical seasons on the Julian scheme. On average, the astronomical s and the es advance by about 11 minutes per year against the Julian year. As a result, the calculated date of gradually moved out of phase with the moon. While and presumably  were aware of the discrepancy, although not of its correct value, it was evidently felt to be of little importance at the time of the Julian reform. However, it accumulated significantly over time: the Julian calendar gained a day about every 134 years. By 1582, it was ten days out of alignment.

The was soon adopted by most Catholic countries (e.g. Spain, Portugal, Poland, most of Italy). Protestant countries followed later, and the countries of Eastern Europe even later. In the (including the ), Wednesday   was followed by Thursday. For 12 years from  used a, and adopted the Gregorian calendar in , but  remained on the Julian calendar until , after the  (which is thus called the '' though it occurred in Gregorian November), while  continued to use it until. During this time the Julian calendar continued to diverge from the Gregorian. In 1700 the difference became 11 days; in 1800, 12; and in 1900, 13, where it will stay till 2100.

Although all countries (most of them in  or ) had adopted the Gregorian calendar by 1927, their national churches had not. A was proposed during a synod in  in May 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. All Orthodox churches refused to accept the lunar part, so almost all Orthodox churches continue to celebrate Easter according to the Julian calendar (the uses the Gregorian Easter).

The solar part of the revised Julian calendar was accepted by only some Orthodox churches. Those that did accept it, with hope for improved dialogue and negotiations with the Western denominations, were the Ecumenical Patriarchate of, the Patriarchates of , , the Orthodox Churches of , , , , (the last in 1963), and the  (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, Gregorian until 2800. The Orthodox Churches of, , , , , , and the continue to use the Julian calendar for their fixed dates, thus they celebrate the Nativity on  Julian (which is  Gregorian until 2100).

In Northern Africa, the Julian calendar (the ) is still in use for agricultural purposes, and is called فلاحي fellāhī "peasant" or sاﻋﺠﻤﻲ a c jamī "not Arabic". The first of yennayer currently corresponds to January 14 and will do until 2100.