History of calendars

Methods of timekeeping can be reconstructed for the prehistoric period from at least the Neolithic. The natural units for timekeeping used by most historical societies are the day, the solar year and the lunation. Calendars are explicit schemes used for timekeeping. The first recorded calendars date to the Bronze Age, dependent on the development of writing in the Ancient Near East, the Egyptian and Sumerian calendars. A larger number of calendar systems of the Ancient Near East becomes accessible in the Iron Age, based on the Babylonian calendar. This includes the calendar of the Persian Empire, which in turn gave rise to the Zoroastrian calendar as well as the Hebrew calendar.

A great number of Hellenic calendars develop in Classical Greece, and with the Hellenistic period also influence calendars outside of the immediate sphere of Greek influence, giving rise to the various Hindu calendars as well as to the ancient Roman calendar.

Calendars in antiquity were usually lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years. This was mostly based on observation, but there may have been early attempts to model the pattern of intercalation algorithmically, as evidenced in the fragmentary 2nd-century Coligny calendar. Nevertheless, the Roman calendar contained very ancient remnants of a pre-Etruscan 10-month solar year.

The Roman calendar was reformed by Julius Caesar in 45 BC. The Julian calendar was no longer dependent on the observation of the new moon but simply followed an algorithm of introducing a leap day every four years. This created a dissociation of the calendar month from the lunation. The Gregorian calendar was introduced as a refinement of the Julian calendar in 1582 and is today in worldwide use as the de facto calendar for secular purposes.

The term calendar itself is taken from calendae, the term for the first day of the month in the Roman calendar, related to the verb calare "to call out", referring to the "calling" of the new moon when it was first seen. Latin calendarium meant "account book, register" (as accounts were settled and debts were collected on the calends of each month). The Latin term was adopted in Old French as calendier and from there in Middle English as calender by the 13th century (the spelling calendar is early modern).

Prehistory

A number of prehistoric structures have been proposed as having had the purpose of timekeeping (typically keeping track of the course of the solar year). This includes many megalithic structures, and reconstructed arrangements going back far into the Neolithic period.

A mesolithic arrangement of twelve pits and an arc found in Warren Field, Aberdeenshire, Scotland, dated to roughly 10,000 years ago, has been described as a lunar calendar and dubbed the "world's oldest known calendar" in 2013.

Ancient Near East

Main articles: Sumerian calendar and Egyptian calendar

The ancient Sumerian calendar divided a year into 12 lunar months of 29 or 30 days. Each month began with the sighting of a new moon. Sumerian months had no uniform name throughout Sumer because of the religious diversity. This resulted in scribes and scholars referring to them as "the first month", "the fifth month" etc. To keep the lunar year of 354 days in step with the solar year of 365.25 days an extra month was added periodically, much like a Gregorian leap year. Also, every six years the Sumerian calendar included an extra month of 62 days.
There were no weeks in the Sumerian calendar. Holy days and time off from work were usually celebrated on the first, seventh and fifteenth of each month. In addition to these holy days, there were also feast days which varied from city to city. A day was divided into twelve hours, six daylight hours, each lasting one-sixth of the day, and six nighttime hours, each lasting one-sixth of the night. This meant the length of hours varied from month to month, daylight hours being shorter in the winter and longer in the summer and vice versa.

Antiquity

China

Main article: Chinese calendar

Before the Spring and Autumn period, the Chinese Calendars were solar calendars. In the so-called five-phase calendar, the year consists of 10 months and a transition, each month being 36 days long, and the transitions 5 or 6 days. During the Warring States period, the primitive lunisolar calendars were established under the Zhou Dynasty, known as the six ancient calendars (simplified Chinese: 古六历; traditional Chinese: 古六曆 The months of these calendars begin on the day with the new moon, with 12 or 13 months (lunations) in a year. The intercalary month is placed at the end of the year. In Qin China, the Qin calendar (simplified Chinese: 秦历; traditional Chinese: 秦曆) was introduced. It follows the rules of Zhuanxu's calendar, but the months order follows the Xia's calendar.

Babylonia and Persia

Further information: Babylonian calendar and Zoroastrian calendar

Classical Greece

The Greeks, as early as the time of Homer, appear to have been familiar with the division of the year into the twelve lunar months but no intercalary month Embolimos or day is then mentioned. Independent of the division of a month into days, it was divided into periods according to the increase and decrease of the moon. Thus, the first day or new moon was called Noumenia. The month in which the year began, as well as the names of the months, differed among the states, and in some parts even no names existed for the months, as they were distinguished only numerically, as the first, second, third, fourth month, etc.

The ancient Athenian calendar was a lunisolar calendar with 354 day years, consisting of twelve months of alternating length of 29 or 30 days. To keep the calendar in line with the solar year of 365.25 days, an extra, intercalary month was added in every other year. The Athenian months were called Hekatombion, Metageitnion, Boedromion, Pyanepsion, Maimakterion, Poseidon, Gamelion, Anthesterion, Elaphebolion, Munychion, Thargelion, and Skirophorion. The intercalary month usually came after Poseidon, and was called second Poseidon.

In addition to their regular, "festival" calendar, the Athenians maintained a second, political calendar . This "conciliar" calendar divided the year into "prytanies", one for each of the "phylai", the subdivisions of Athenian citizens. The number of phylai, and hence the number of prytanies, varied over time. Until 307 BC, there were 10 phylai. After that the number varies between 11 and 13 (usually 12). Even more confusing, while the conciliar and festival years were about the same length in the 4th century BC, such was not regularly the case earlier or later. Documents dated by prytany are frequently very difficult to assign to a particular equivalent in the Julian calendar.

The table of Greek Olympiads, following the four-year cycles between the Olympic Games from 1 July 776 BC, continued until the end of the 4th century AD. The Babylonian Era of Nabonassar, beginning on 26 February 747 BC, was used by the Greeks of Alexandria. It was later known in the Middle Ages from the works of Ptolemy.

Hellenistic period

Further information: Roman calendar

The Greek calendars were greatly diversified by the Hellenistic period, with separate traditions in every Greek state. Of primary importance for the reconstruction of the regional Greek calendars is the calendar of Delphi, because of the numerous documents found there recording the manumission of slaves, many of which are dated both in the Delphian and in a regional calendar.

The Macedonian Era of the Seleucids, which began with the conquest of Babylon by Seleucus Nicator in 312 BC. It became widely used in the Levant. The Jews knew it as the "era of contracts", and used it in Europe until the 15th century.

The Roman Republican calendar numbered years based on the sitting consuls. References to the year of consulship were used in both conversation and official records. Romans from the same family often had the same praenomen, which sometimes makes it difficult to distinguish them, and there were two consuls at any one time, each of whom might sometimes hold the appointment more than once, meaning that it was (and is) necessary to be well educated in history to understand the references. The Romans had an eight-day week, with the market-day falling every eight days. It was called a nundinum or 'nine-day' in inclusive counting.

Most of the regional Hindu calendars are inherited from a system standardized in classical Hindu astronomy as adopted via Indo-Greek transmission in the final centuries BC, and reformed by Gupta era astronomers such as Āryabhaṭa and Varāhamihira.

Roman Empire

Main article: Julian calendar

The old Roman year had 304 days divided into 10 months, beginning with March. The extra months Ianuarius and Februarius had been invented as stop-gaps. Julius Caesar realized that the system had become inoperable, so he effected drastic changes in the year of his third consulship. The New Year in 709 AUC began on 1 January and ran over 365 days until 31 December. Further adjustments were made under Augustus, who introduced the concept of the "leap year" in 737 AUC (AD 4). The resultant Julian calendar remained in almost universal use in Europe until 1582.

Marcus Terentius Varro introduced the Ab urbe condita epoch, assuming a foundation of Rome in 753 BC. The system remained in use during the early medieval period until the widespread adoption of the Dionysian era in the Carolingian period. In the Roman Empire, the AUC year could be used alongside the consular year, so that the consulship of Quintus Fufius Calenus and Publius Vatinius could be determined as 707 AUC (or 47 BC), the third consulship of Caius Julius Caesar, with Marcus Aemilius Lepidus, as 708 AUC (or 46 BC), and the fourth consulship of Gaius Julius Caesar as 709 AUC (or 45 BC).

The seven-day Week has a tradition reaching back to the Ancient Near East, but the introduction of the "planetary week" which remains in modern use dates to the Roman Empire period (see also names of the days of the week).

Middle Ages

The page for May in the Bedford Psalter and Hours ms. (British Library Add MS 42131, fol. 3r, early 15th century)

Christian Europe

Main article: Anno Domini

For the first six centuries since the birth of Jesus Christ, European countries used various local systems to count years, most usually regnal years, modeled on the Old Testament. In some cases, Creation dating was also used. In the 6th century, the Christian monk Dionysius Exiguus devised the Anno Domini system, dating from the Incarnation of Jesus. In the 8th century, the Anglo-Saxon historian Bede the Venerable used another Latin term, "ante uero incarnationis dominicae tempus" ("the time before the Lord's true incarnation", equivalent to the English "before Christ"), to identify years before the first year of this era.

According to the Catholic Encyclopedia, even Popes continued to date documents according to regnal years, and usage of AD only gradually became common in Europe from the 11th to the 14th centuries. In 1422, Portugal became the last Western European country to adopt the Anno Domini system.

In 1267, the medieval scientist Roger Bacon stated the times of full moons as a number of hours, minutes, seconds, thirds, and fourths (horae, minuta, secunda, tertia, and quarta) after noon on specified calendar dates. Although a third for ​¹⁄₆₀ of a second remains in some languages, for example Polish tercja and Arabic ثالثة, the modern second is further divided decimally.

Rival calendar eras to Anno Domini remained in use in Christian Europe. In Spain, the "Era of the Caesars" was dated from Octavian's conquest of Iberia in 39 BC. It was adopted by the Visigoths and remained in use in Catalonia until 1180, Castille until 1382 and Portugal until 1415.

For chronological purposes, the flaw of the Anno Domini system was that dates have to be reckoned backwards or forwards according as they are BC or AD. According to the Catholic Encyclopedia, "in an ideally perfect system all events would be reckoned in one sequence. The difficulty was to find a starting point whence to reckon, for the beginnings of history in which this should naturally be placed are those of which chronologically we know least." For both Christians and Jews, the prime historical date was the Year of Creation, or Annus Mundi. The Byzantine Church fixed the date of Creation at 5509 BC. This remained the basis of the ecclesiastical calendar in the Greek and Russian Orthodox world until modern times. The Coptic Church fixed on 5500 BC. Later, the Church of England, under Archbishop Ussher in 1650, would pick 4004 BC. Jewish scholars preferred 3761 BC as the date of creation, which forms the basis of the modern Jewish calendar. However, "any attempt thus to determine the age of the world has been long since abandoned."

Islamic calendar

The Islamic calendar is based on the prohibition of intercalation (nasi') by Muhammad, in Islamic tradition dated to a sermon held on 9 Dhu al-Hijjah AH 10 (Julian date: 6 March 632). This resulted in an observationally based lunar calendar shifting relative to the seasons of the solar year.

Icelandic calendar

Main article: Icelandic calendar

In medieval Iceland, a calendar was introduced in the 10th century. While the ancient Germanic calendars were based on lunar months, the new Icelandic calendar introduced a purely solar reckoning, with a year having a fixed number of weeks (52 weeks or 364 days). This necessitated the introduction of "leap weeks" instead of the Julian leap days.

Hindu calendars

Main article: Hindu calendar

Various Hindu calendars developed in the medieval period, with Gupta era astronomy as their common basis. Some of the more prominent regional Hindu calendars include the Nepali calendar, Assamese calendar, Bengali calendar, Malayalam calendar, Tamil calendar, Vikrama Samvat used in Northern India, and Shalivahana calendar in the Deccan States of Karnataka, Telangana, Maharashtra and Andhra Pradesh. The common feature of all regional Hindu calendars is that the names of the twelve months are the same (because the names are based in Sanskrit) though the spelling and pronunciation have come to vary slightly from region to region over thousands of years. The month which starts the year also varies from region to region. The Buddhist calendar and the traditional lunisolar calendars of Cambodia, Laos, Myanmar, Sri Lanka and Thailand are also based on an older version of the Hindu calendar.

Mesoamerica

Main article: Mayan calendar

Of all the ancient calendar systems, the Maya and other Mesoamerican systems are the most complex. The Mayan calendar had 2 years, the 260-day Sacred Round, or tzolkin, and the 365-day Vague Year, or haab.

A modern pictogram of the Mayan god Ahau, after which the 20th day of the tzolkin cycle was named

The Sacred Round of 260 days is composed of two smaller cycles: the numbers 1 through 13, coupled with 20 different day names: Imix, Ik, Akbal, Kan, Chicchan, Cimi, Manik, Lamat, Muluc, Oc, Chuen, Eb, Ben, Ix, Men, Cib, Caban, Eiznab, Cauac, and Ahau. The Sacred Round was used to determine important activities related to the gods and humans: name individuals, predict the future, decide on auspicious dates for battles, marriages, and so on.

The two cycles of 13 and 20 intermesh and are repeated without interruption: the cycle would begin with 1 Imix, then 2 Ik, then 3 Akbal and so on until the number 13 was reached, at which point the number cycle was restarted so 13 Ben would be followed by 1 Ix, 2 Men and so on. This time Imix would be numbered 8. The cycle ended after 260 days, with the last day being 13 Ahau.

The Vague Year of 365 days is similar to our modern calendar, consisting of 18 months of 20 days each, with an unlucky five-day period at the end. The Vague Year had to do primarily with the seasons and agriculture, and was based on the solar cycle. The 18 Maya months are known, in order, as: Pop, Uo, Zip, Zotz, Tzec, Xuc, Yaxkin, Mol, Chen, Yax, Zac, Ceh, Mac, Kankin, Maun, Pax, Kayab and Cumku. The unlucky five-day period was known as Uayeb, and was considered a time which could hold danger, death and bad luck.

The Vague Year began with the month of Pop. The Maya 20-day month always begins with the seating of the month, followed by days numbered 1 to 19, then the seating of the following month, and so on. This ties in with the Maya notion that each month influences the next. The Maya new year would start with 1 Pop, followed by 2 Pop, all the way through to 19 Pop, followed by the seating of the month of Uo, written as 0 Uo, then 1 Uo, 2 Uo and so on. These two cycles coincided every 52 years. The 52-year period of time was called a "bundle" and was similar to a modern-day century.

Modern calendars

Further information: List of calendars and Calendar reform

While the Gregorian calendar is now in worldwide use for secular purposes, various medieval or ancient calendars remain in regional use for religious or social purposes, including the Julian calendar, the Hebrew calendar, the Islamic calendar, various Hindu calendars, the Zoroastrian calendar etc.

There are also various modern calendars that see limited use, either created for the use of new religious movements or reformed versions of older religious calendars, or calendars introduced by regionalist or nationalist movements.

• Javanese calendar (1633)
• Jōkyō calendar (1685)
• French Republican calendar (1793)
• Baha'i calendar (1873)
• Solar Hijri calendar (1925)
• Indian national calendar (1957)
• Discordian calendar (1963)
• Juche Era calendar (1997)

See also

• Week-day names
• History of timekeeping devices