Epochs and Eras

In many calendars years are counted beginning from an event which is considered to be of great importance. The point in time on which the counting starts is called the epoch, or era of a calendar. There are two main groups of such eras; one contains eras related to a real event. This can be the beginning of the reign of a king or emperor, a victory in a battle, or the proclamation of a new state or government. The other group is formed by eras with a more religious background which mainly begin to count the years from the creation or the beginning of the world.

Some of these eras are shortly described here.

Real Event Eras


The Olypiads as a time unit are attributed to the Greek historian Timaios who lived in the 4th and 3rd century BCE. Erathostenes slightly modified this reckoning later. In ancient Greece years were designated with the names of the holders of an office which were changed every year. This method was hardly practicable for historians, which is why Timaios was looking for a possibility to designate years in a simple manner understood by all Greeks. Every four years, Olympic games were held with the champions recorded since 776 BCE. There were Olympic games before 776 BCE, but no reports are known of these. Thus Timaios started his counting in this year calling it the first year of the first Olympiade. The following year was the second year of the first Olympiade, then came the third year. In 772 BCE, Olympic games were held again; Timaios called this year the first year of the second Olympiade.

Although this reckoning still was too complicated to become common, historians used it even until the time after the Romans had conquered Greece. After the Olympic games had been forbidden by emperor Theodosius in 394 BCE, no games were held until the first New Olympic games took place in Athens in 1896.

Foundation Era (of the City of Rome)

Computed by Atticus and published by M. Terentius Varro, the foundation of Rome was considered to have taken place on 21 April 753 BCE. In historical records, the years were counted according to this era and marked with the words ‘ab urbe condita’ (abbr. a. u. c.), meaning ‘after the foundation of the city’.

Sometimes, another Era was used, beginning a year later than the so-called Varronian Era described above. This Era (the Capitolinian Era) begins with the year 752 BCE and was used in lists of consuls, which began their terms on 15 March, the civil year beginning on 1 January already. This could be the reason for the difference between the two eras.

Nabonassar Era

In the fourth century BCE, Egyptian astronomers began to use an era based on the reign of the Babylonian king Nabonassar, which came to power in 747 BCE. Not the years, but regnal years of the most important king in the Middle East were counted. In the beginning, this was Nabonassar, later the Assyrian, Persian, and Macedonian kings. Eventually, beginning with Augustus, the Roman emperors' regnal years were recorded. The years were Egyptian years with an invariable length of 365 days. The first year of the reign of a certain king was 1 Thot of the year in which he took power. Thus, the Nabonassar era is 26 February 747 BCE.

The lists with regnal years were recorded until the third century  CE.

Buddha Era

This era, 544 BCE, is used in Sri Lanka and replaced an earlier Buddha Era which counted its years from 483 BCE.

Mahâvîra Era

Vardhamâna Mahâvîra, founder of the Jain religion, was born in 540 BCE and lived a life of ascetiscism for more than ten years. Later he teached Jainism until his death (about 468 BCE). The era starts in 528 BCE and is in use for religious purposes.

Seleucid Era 

Soon after Alexander the Great's death, his military leaders fought each other to get their own parts of the empire. The ‘diadochs’ (Greek ‘successors’) had divided the vast empire before, but no one was really satisfied with what he got. Of the emerging states, the Seleucid empire reigned by a dynasty beginning with Seleucos, became the mightiest one. The Seleucid Era begins in 312 BCE, probably with a victory of Seleucos in a battle. The exact era is depending on the calendar it is used for. In Syria the year began in autumn, thus the era is in autumn 312 BCE, while in Babylon the first year of this counting began in spring 311 BCE, half a year later than in Syria.

The use of this era spread rapidly all over the Middle East. Even after the end of the Seleucid empire, in the Jewish calendar the years were counted using the Seleucid era.

Vikrama Era

According to tradition, this era was founded by a king named Vikramâditya. He is said to have freed the city of Ujjayinî of the Shaka. The years are counted beginning in 58 BCE. So far king Vikramâditya could not be identified with any historic king. King Chandra Gupta II. had the title Vikramâditya and conquered Ujjayinî but lived about 400 years after the epoch. The era is called krita (=‘established’) in the earliest inscripts in which it is used.
The shaka era was first used mainly in northern India, where the years began with the month Kârttika. In the Medieval the years were reckoned to begin with the bright half of Chaitra here, whereas in southern India the year began with the dark half of that month. For religios purposes the Vikrama era is still in use today.

Shaka Era

Supposedly founded by a Shaka king after his conquest of Ujjayinî 137 years after Vikramâditya had taken the city according to tradition, the era actually starts with the year 78 CE. Obviously, the era was created by the Kushan king Kanishka, whose father and grandfather have brought north west India under their rule. There it was in use and later spread over the whole Indian subcontinent and south east Asia. It is still employed for religious purposes today and was choses for the Indian National Calendar, see Calendars in India

Christian Era

The Christian Era was first used by Dionysius Exiguus in his Easter tables, which he established in 525. The era start with Christ's birth, placed in the year 1 CE and became common from the 9th century. It is used in the Julian calendar and the Gregorian calendar.


Perhaps created by the small Traikûtaka dynasty the era beginning in 248 CE was in use in central India until Islamic rule.

Era of Diocletian 

In 284 CE, Diocletian became Roman emperor. During his reign, reforms were carried out in the army, in the financial system, and in the administration of the Roman empire. Diocletian also tried to reinstitute the old Roman religion. In 303 and 04 CE, four anti-Christian laws were published, which led to brutal repressions against Christians especially in the eastern part of the empire.

Nevertheless, Christians began to count years from the beginning of the reign of their suppressor. New Year's day of the (adapted) Egyptian calendar that year was 29 August 284 CE, which became the epoch of the era of Diocletian. This era is still used by Coptic Christians, who call it ‘Era of Martyrs’. In Europe, this era was used until the 6th century.

Gupta Era

Probably founded by Chandra Gupta I this era starts in 320 CE, supposedly the year Chandra Gupta came to power. The era was used in the Gupta empire and later in Gujarat.

Harsha Era

The reign of king Harshavardhana in Kânyakubja (today Kanauj) began in 606 CE. Harshavardhana ruled over Kânyakubja, which was one of the kingdoms the Gupta empire had split into, until 647. His era lived until about 800 in northern India.

Islamic Era (Hijra)

The Islamic era begins with 16 July 622, Julian, although sometimes 15 July 622 is regarded as the beginning of that era. But, with the religious Islamic calendar being observation-based, this is insignificant for determining the current date. The fixed Islamic calendar begins with 16 July 622, Julian. The epoch starts with the day the prophet Muhammad moved from Mekkah to Madinah, then called Yathrib.

As in the Islamic calendar, in the Persian calendar the years are counted beginning with the Julian year 622. But the exact epoch is not 15 or 16 July, but 19 March 622, Julian, the day of the vernal equinox that year. With the Persian calendar counting solar years and the Islamic calendar counting lunar years, August 2003 of the Gregorian calendar lies in the Persian year 1382, while the Islamic calendar is in its year 1421.

Japanese Imperial Era

This era starts on 1 January of the year 661 in which according to tradition the Japanese Empire was established. It was frequently used from 1873 to 1945 in connection with the Gregorian calendar.

Republican Era

This era, beginning on 22 September 1792, Gregorian, was used in the French Revolutionary calendar from November 1795 until December 1805, Gregorian. It begins with the day the Republic was declared, which happened to be the day of the autumnal equinox of 1792. The years were counted as ‘years of the Republic’ and written as Roman numbers.

Minguo Era

This era may be translated as ‘Era of the Republic’ and was introduced by the republican Chinese government in China. It starts on 1 January 1912 and was used in mainland China until 1949. On Taiwan it is in use still today.

OF Era ;-)

On 1 September 1988, the professional education of the creators of the OF calendar started. Therefore the Stresse are counted from that day.

Eras of Legendary Events

Unlike the eras mentioned above, these eras begin their count with legendary events, the exact date being computed from data extracted from the Bible, other religious documents, and lists of kings.

Alexandrinian World Era

This era assumes Creation on 29 August 5493 BCE and is based on a proposal of Annianus (see below). Only the beginning of the year was aligned to the civil 29. August. This era was used mainly by Egyptian chronologists, but soon replaced by the Greek or Byzantine Era.

Greek or Byzantine World Era

This era begins on 1 September 5509 BCE, which was the day of the Creation, according to Byzantine historians. It was officially in use in Byzantium until it was destroyed in 1453. From here, it came to Russia, where it was replaced by the Christian era as late as 1 January 1700, Julian.

Other World Eras

Sextus Julius Africanus fixed 25 March 5501 BCE as the date of the Creation in the 3rd century. Eusebius proposed his World Era starting in 5200 BCE in the 5th century, while his contemporary Annianus, an Egyptian monk, advocated 25 March 5492 BCE. At the same time, the Alexandrinian monk Panodoros proposed 19 March 5493 BCE.

Jewish Creation Era

The Talmud consideres the 400th year after the destruction of the Second Temple (i. e. 470 CE) to be the year 4231 after the creation of the world. Thus, the Jewish Creation Era was first mentioned in the 5th century. There have been several computations, fixing the Creation somewhere in the years 3762 until 3758 BCE. Eventually, the era now in use was established, which is Sunday, 6 October 3761 BCE, at 23:11:20 hours. According to the Jewish time units, this is Monday, 5 hours and 204 parts (s. Jewish calendar).

Other World Eras

Sextus Julius Africanus fixed 25 March 5501 BCE as the date of the Creation in the 3rd century. Eusebius proposed his World Era starting in 5200 BCE in the 5th century, while his contemporary Annianus, an Egyptian monk, advocated 25 March 5492 BCE. At the same time, the Alexandrinian monk Panodoros proposed 19 March 5493 BCE.

Eras of other Legendary Events

Christian writers also used the era of Abraham, placed in 2016 BCE by Eusebius. Also several Passion eras are to be found, e. g. starting in 28 CE or in 24 CE. Furthermore, an era starting with the Exodus of the Children of Israel (ab Exodo) was in use, beginning in 1552 BCE.

The Mayans started their Long Count somewhere in the 4th millenium BCE. According to Goodman-Martinez-Thompson correlation the start point fell on 6 September 3114 BCE (JD 584283). At the end of each Long Count (of 1872000 days) according to tradition the world will be destroyed to be recreated.


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