Calendars and Writing History

Methods of timekeeping can be reconstructed for the prehistoric period from at least the Neolithic period. The natural units for timekeeping used by most historical societies are the day, the solar year, and the lunation. The first recorded calendars date to the Bronze Age, and include the Egyptian and Sumerian calendars. A larger number of calendar systems of the Ancient Near East became accessible in the Iron Age and were based on the Babylonian calendar. One of these was 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 were developed in Classical Greece and influenced calendars outside of the immediate sphere of Greek influence. These gave rise to the various Hindu calendars, as well as to the ancient Roman calendar, which contained very ancient remnants of a pre-Etruscan ten-month solar year. The Roman calendar was reformed by Julius Caesar in 45 BCE. 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.

Despite various calendars used across millennia, cultures, and geographical regions, Western historical scholarship has unified the standards of determining dates based on the dominant Gregorian calendar. Regardless of what historical period or geographical areas Western historians investigate and write about, they adjust dates from the original timekeeping system to the Gregorian calendar. Occasionally, some historians decide to use both dates: the dates recorded under the original calendar used, and the date adjusted to the Gregorian calendar, easily recognizable to the Western student of history.

Julian Calendar

The old Roman year had 304 days divided into ten months, beginning with March. However, the ancient historian, Livy, gave credit to the second ancient Roman king, Numa Pompilious, for devising a calendar of twelve months. The extra months Ianuarius and Februarius had been invented, supposedly by Numa Pompilious, 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 (ab urbe condita—
year from the founding of the City of Rome) began on January first and ran over 365 days until December 31. Further adjustments were made under Augustus, who introduced the concept of the leap year in 737 AUC (4 CE). 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 BCE. The system remained in use during the early medieval period until the widespread adoption of the Dionysian era in the Carolingian period. 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.

Gregorian Calendar

The Gregorian calendar, also called the Western calendar and the Christian calendar, is internationally the most widely used civil calendar today. It is named after Pope Gregory XIII, who introduced it in October, 1582. The calendar was a refinement to the Julian calendar, amounting to a 0.002% correction in the length of the year. The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices—particularly the vernal equinox, which set the date for Easter celebrations. Transition to the Gregorian calendar would restore the holiday to the time of the year in which it was celebrated when introduced by the early Church. The reform was adopted initially by the Catholic countries of Europe. Protestants and Eastern Orthodox countries continued to use the traditional Julian calendar, and eventually adopted the Gregorian reform for the sake of convenience in international trade. The last European country to adopt the reform was Greece in 1923.

Calendars Outside of Europe

While the European Gregorian calendar eventually dominated the world and historiography, a number of other calendars have shaped timekeeping systems that are still influential in some regions of the world.
The Islamic calendar determines the first year in 622 CE, during which the emigration of Muhammad from Mecca to Medina, known as the Hijra, occurred. It is used to date events in many Muslim countries (concurrently with the Gregorian calendar), and is used by Muslims everywhere to determine the proper days on which to observe and celebrate Islamic religious practices (e.g., fasting), holidays, and festivals.

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, the Vikrama Samvat (used in Northern India), and Shalivahana calendar. 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) although the spelling and pronunciation have come to vary slightly from region to region over thousands of years. The month that 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.

Of all the ancient calendar systems, the Mayan and other Mesoamerican systems are the most complex. The Mayan calendar had two years, the 260-day Sacred Round, or tzolkin, and the 365-day Vague Year, or haab.
The essentials of the Mayan calendar are based upon a system that was in common use throughout the region, dating back to at least the fifth century BCE. It shares many aspects with calendars employed by other earlier Mesoamerican civilizations, such as the Zapotec and Olmec, and contemporary or later ones, such as the Mixtec and Aztec calendars. The Mayan calendar is still used in many modern communities in the Guatemalan highlands, Veracruz, Oaxaca and Chiapas, Mexico.

Anno Domini v. Common Era

The terms anno Domini (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars. The term anno Domini is Medieval Latin, which means in the year of the Lord, but is often translated as in the year of our Lord. It is occasionally set out more fully as anno Domini nostri Iesu (or Jesu Christi (“in the year of Our Lord Jesus Christ”). Dionysius Exiguus of Scythia Minor introduced the AD system in AD 525, counting the years since the birth of Christ. This calendar era is based on the traditionally recognized year of the conception or birth of Jesus of Nazareth, with AD counting years after the start of this epoch and BC denoting years before the start of the era. There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC. This dating system was devised in 525, but was not widely used until after 800.

A calendar era that is often used as an alternative naming of the anno Domini
is Common Era or Current Era, abbreviated CE. The system uses BCE as an abbreviation for “before the Common (or Current) Era.” The CE/BCE designation uses the same numeric values as the AD/BC system so the two notations (CE/BCE and AD/BC) are numerically equivalent. The expression “Common Era” can be found as early as 1708 in English and traced back to Latin usage among European Christians to 1615, as vulgaris aerae, and to 1635 in English as Vulgar Era.
Since the later 20th century, the use of CE and BCE have been popularized in academic and scientific publications, and more generally by authors and publishers wishing to emphasize secularism or sensitivity to non-Christians, because the system does not explicitly make use of religious titles for Jesus, such as “Christ” and Dominus (“Lord”), which are used in the BC/AD notation, nor does it give implicit expression to the Christian creed that Jesus is the Christ. While both systems are thus an accepted standard, the CE/BCE system is more neutral and inclusive of a non-Christian perspective.

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