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 astronomer
Sosigenes of Alexandria 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.
Although the Julian calendar remained in use into the
20th century in some countries and is still used by many national Orthodox churches, it has generally been replaced by the modern
Gregorian calendar. Reform was required because too many leap days are added with respect to the astronomical seasons on the Julian 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" (NS), 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.
|
Bust of Julius Caesar from the Altes Museum in Berlin. |
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, which were 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.
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 365¼ 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 Julius Caesar's pontificate,
63 BC 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 Julian reform was intended to correct this problem permanently. Before it took effect, the missed intercalations during Julius Caesar's pontificate were made up by inserting 67 days (22+23+22) between November and December of 46 BC in the form of two months, in addition to 23 days which had already been added to February. Thus 90 days were added to this last year of the Roman Republican calendar, giving it 445 days. Because it 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.
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.
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 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
153 BC.
The Romans later renamed months after
Julius 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
16th 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).
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:
30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29 - totaling 354 days.
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
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 calendar predating the Julian reform has survived [
1]which confirms the literary accounts that the months were already irregular before Julius Caesar reformed it:
29, 28, 31, 29, 31, 29, 31, 29, 29, 31, 29, 29
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.
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,
Censorinus, writing in the third century AD, states that, in his time, the AUC year began with the
Parilia, celebrated on
21 April, which was regarded as the actual anniversary of the foundation of Rome. This prevented the early Roman church from celebrating Easter after
21 April because the festivities associated with the
Parilia 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
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
525 Dionysius Exiguus proposed the system of
anno Domini, which gradually spread through the western Christian world, once the system was adopted by
Bede. The
Julian start of the year was, at first, set to the traditional date of the incarnation, or annunciation, of
Jesus on
25 March, although this soon changed to Christmas, then back to Annunciation Day in England, and for a time the numbered year even began on Easter in France.
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 Wednesday
2 September 1752 followed by Thursday
14 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 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
Constantinople, the Patriarchates of
Alexandria,
Antioch, the Orthodox Churches of
Greece,
Cyprus,
Romania,
Poland,
Bulgaria (the last 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 (which is
7 January Gregorian until 2100).
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