It was the learned Christian monk Dionysius Exiguus who invented the Christian calendar exactly 1,500 years ago, in the year 525 AD.
The fact that he was probably not entirely correct in his calculations is another matter.
The Christians living in the Roman Empire had initially adopted the Roman calendar, which referred to the mythical founding of the city of Rome (the mnemonic verse: 753 - Rome crawled out of the egg).
Then some began to calculate the years according to the "martyr era": The beginning was placed at the inauguration of the Roman Emperor Diocletian in 284 AD, who created numerous martyrs through his brutal persecutions of Christians. The Coptic and Ethiopian Orthodox Churches still count as such today.
However, from the point of view of some Christians, it was not appropriate to organise time according to the godless Roman emperor.
Whoever sets the calendar has power. However, the Roman Empire in Western Europe had disintegrated under the onslaught of Germanic peoples, while the Eastern Roman Empire in Constantinople flourished.
The Roman Pope showed ambitions to change this. He also wanted to prove his claim to leadership within the Church. Early Christianity was fragmented and still far removed from a firmly established church organisation and doctrine. This fragmentation was particularly evident in the determination of the date of Easter, on which the bishops and patriarchs of Christendom were often unable to agree.
The right man at the right time
In this difficult situation, Dionysius came at just the right time: born on the western shore of the Black Sea, he had enjoyed a comprehensive classical Hellenistic education in the Greek East and made a name for himself as a translator of Greek texts into Latin. He is regarded as one of the most important mediators between the Greek and Latin intellectual worlds.
Around the year 496, he came to Rome to translate the sources of the early councils and canon law written in Greek into Latin on behalf of the Pope - a work that strengthened the Pope's position of power, as it enabled him to draw on a wealth of knowledge in any religious or ecclesiastical-political dispute.
Pope John I also drew on Dionysius in the dispute over the dates of Easter in 525. The erudite monk buried himself in old files and referred to resolutions of the famous Council of Nicaea from the year 325 in order to calculate the dates of Easter for the following 95 years. This brought peace to Christianity.
During his studies, the monk also came to the conclusion that a new calendar was overdue. He was convinced that the new Christian era should begin with the year of Christ's birth. Dionysius calculated the supposed date of Jesus' birth and thus the year one from the sparse time data in the Gospels and the Acts of the Apostles. He placed himself in the year 525 after the birth of Christ.
This calendar became established throughout Europe from the 8th century and later throughout the entire Christianised world. Today it is clear that the calculations of Dionysius Exiguus were on shaky ground.
If you compare the few dates in the Gospels with the historical facts, contradictions emerge: the biblical infanticide Herod died four years before the birth of Christ. Many historians therefore come to the conclusion that Jesus must have been born between 7 and 4 BC.
And then there is the problem with the zero.
As the Romans did not know this number, Dionysius labelled the year of Jesus' birth as the year one.
This becomes problematic if, as soon happened, the Christian calendar is extended to pre-Christian times.
The year 1 AD immediately follows the year 1 BC.
There are therefore only three years between the beginning of the year 2 BC and the year 2 AD and not four years.
But this is only a minor flaw.