The calendar is based on the initial calculations made by
Panodorus of Alexandria (late 4th century), and an early discussion of it appears in a treatise by
George Syncellus (7th century), who mentions all the main variants of the "World Era" in his work.
 Georgios argues that the main advantage of the World era is the common starting point of the astronomical
solar cycles, and of the cycle of
indictions, the usual dating system in Byzantium since the 6th century. He also already regards it as the most convenient for the
computus. Complex calculations of the 19-year lunar and 28-year solar cycles within this world era allowed scholars to discover the cosmic significance of certain historical dates, such as the
birth or the
crucifixion of Jesus.
This date underwent minor revisions before being finalized in the mid-7th century, although its precursors were developed c. AD 412 (see
Alexandrian Era). By the second half of the 7th century, the Creation Era was known in
Western Europe, at least in Great Britain.
[note 3] By the late 10th century around AD 988, when the era appears in use on official government records, a unified system was widely recognized across the Eastern Roman world.
The era was ultimately calculated as starting on September 1, and
Jesus was thought to have been born in the year 5509 since the creation of the world.
 Historical time was thus calculated from the creation, and not from Christ's birth, as in the west. The Eastern Church avoided the use of the
Anno Domini system of
Dionysius Exiguus, since the date of Christ's birth was debated in Constantinople as late as the 14th century. Otherwise the Byzantine calendar was identical to the
Julian Calendar except that:
- the names of the months were transcribed from Latin into Greek;
- the first day of the year was September 1,
[note 4] so that both the Ecclesiastical and Civil calendar years ran from 1 September to 31 August, (see
Indiction), which to the present day is the
- dates were seldom, if ever, reckoned according to the
νωναί, nōnaí), and
εἰδοί, eidoí) of the months in the
Roman manner but simply numbered from the beginning of the month in the
[note 6] and,
- its era was based on the year of creation, reckoned September 1, 5509 BC, to August 31, 5508 BC, rather than the
foundation of Rome; years were also reckoned by their place in the
indiction and not by the years' consuls.
leap day of the Byzantine calendar was obtained in an identical manner to the
bissextile day of the original Roman version of the Julian calendar, by doubling the sixth day before the
calends of March, i.e., by doubling 24 February (numbering the days of a month from its beginning and hence the leap day of 29 February was an invention of the late
The Byzantine World Era was gradually replaced in the
Orthodox Church by the
Christian Era, which was utilized initially by Patriarch Theophanes I Karykes in 1597, afterwards by Patriarch
Cyril Lucaris in 1626, and then formally established by the Church in 1728.
 Meanwhile, as Russia received Orthodox Christianity from Byzantium, she inherited the Orthodox Calendar based on the Byzantine Era (translated into Slavonic). After the collapse of the
Byzantine Empire in 1453, the era continued to be used by Russia, which witnessed millennialist movements in Moscow in AD 1492 (7000 AM) due to the end of the church calendar. It was only in AD 1700 that the Byzantine World Era in Russia was changed to the
Julian Calendar by
Peter the Great.
 It still forms the basis of traditional Orthodox calendars up to today. September AD 2000 began the year 7509 AM.
Earliest Christian sources on the age of the world
The earliest extant Christian writings on the age of the world according to the Biblical chronology are by
Theophilus (AD 115–181), the sixth bishop of Antioch from the Apostles, in his apologetic work To Autolycus,
 and by
Julius Africanus (AD 200–245) in his Five Books of Chronology.
 Both of these early Christian writers, following the
Septuagint version of the
Old Testament, determined the age of the world to have been about 5,530 years at the birth of Christ.
Dr. Ben Zion Wacholder points out that the writings of the
Church Fathers on this subject are of vital significance (even though he disagrees with their chronological system based on the authenticity of the
Septuagint, as compared to that of the
Hebrew text), in that through the Christian chronographers a window to the earlier Hellenistic biblical chronographers
[note 8] is preserved:
- An immense intellectual effort was expended during the Hellenistic period by both Jews and
pagans to date
building of the Temple... In the course of their studies, men such as
Tatian of Antioch (flourished in 180),
Clement of Alexandria (died before 215),
Hippolytus of Rome (died in 235),
Julius Africanus of Jerusalem (died after 240),
Eusebius of Caesarea in Palestine (260–340), and Pseudo-Justin frequently quoted their predecessors, the Graeco-Jewish biblical chronographers of the Hellenistic period, thereby allowing discernment of more distant scholarship.
Demetrius the Chronographer (flourishing 221–204 BC) wrote On the Kings of Judea which dealt with biblical exegesis, mainly chronology; he computed the date of
the flood and the birth of
Abraham exactly as in the
Septuagint, and first established the Annus Adami – Era of Adam, the antecedent of the
Hebrew World Era, and of the
Alexandrian and Byzantine Creation Eras.
The Alexandrian Era (
Greek: Κόσμου ἔτη κατ’ Ἀλεξανδρεῖς, Kósmou étē kat'Alexandreîs) developed in AD 412, was the precursor to the Byzantine Era. After the initial attempts by
Clement of Alexandria and others
[note 9], the Alexandrian computation of the date of creation was worked out to be 25 March 5493 BC.
The Alexandrine monk
Panodorus reckoned 5904 years from Adam to the year AD 412. His years began with August 29, corresponding to the
First of Thoth, the
Egyptian new year.
Annianos of Alexandria however, preferred the Annunciation style as New Year's Day, 25 March, and shifted the Panodorus era by about six months, to begin on 25 March. This created the Alexandrian Era, whose first day was the first day of the proleptic
[note 10] Alexandrian civil year in progress, 29 August 5493 BC, with the ecclesiastical year beginning on 25 March 5493 BC.
- This system presents in a masterly sort of way the mystical coincidence of the three main dates of the world's history: the beginning of Creation, the
Incarnation, and the
Christ. All these events happened, according to the Alexandrian chronology, on 25 March; furthermore, the first two events were separated by the period of exactly 5500 years; the first and the third one occurred on Sunday — the sacred day of the beginning of the Creation and its renovation through Christ
Dionysius of Alexandria had earlier emphatically quoted mystical justifications for the choice of March 25 as the start of the year:
- March 25 was considered to be the anniversary of Creation itself. It was the first day of the year in the medieval
Julian calendar and the nominal vernal equinox (it had been the actual equinox at the time when the Julian calendar was originally designed). Considering that Christ was conceived at that date turned March 25 into the Feast of the
Annunciation which had to be followed, nine months later, by the celebration of the
birth of Christ, Christmas, on December 25.
The Alexandrian Era of March 25, 5493 BC was adopted by church fathers such as
Maximus the Confessor and
Theophanes the Confessor, as well as chroniclers such as
George Syncellus. Its striking mysticism made it popular in Byzantium especially in monastic circles. However this masterpiece of Christian symbolism had two serious weak points: historical inaccuracy surrounding the date of
Resurrection as determined by its
[note 11] and its contradiction to the chronology of the
St John regarding the date of the
Crucifixion on Friday after the Passover.
A new variant of the World Era was suggested in the
Chronicon Paschale, a valuable Byzantine universal chronicle of the world, composed about the year 630 AD by some representative of the Antiochian scholarly tradition.
 It had for its basis a chronological list of events extending from the creation of
Adam to the year AD 627. The chronology of the writer is based on the figures of the Bible and begins with 21 March, 5507.
For its influence on Greek Christian chronology, and also because of its wide scope, the "Chronicon Paschale" takes its place beside
Eusebius, and the chronicle of the monk
 which was so important in the Middle Ages; but in respect of form it is inferior to these works.
By the late 10th century, the Byzantine Era, which had become fixed at September 1 5509 BC since at least the mid-7th century (differing by 16 years from the Alexandrian date, and 2 years from the
Chronicon Paschale), had become the widely accepted calendar of choice par excellence for Chalcedonian Orthodoxy.