What year is it?
How an inexplicable decision 2,000 years ago baked our calendar into every database on Earth
Since the widespread use of social media and the automation of most parts of our lives, we have reached a phase of humanity in which we constantly produce historical evidence. In comparison: we might have a handful of sources telling us about the most important events in a whole ancient kingdom over a decade. But today, we have not only data about a vast majority of all citizens, but also an enormous amount of data produced by many individuals themselves – data about things no historian would ever consider important enough to write into a history book.
By the structure alone of how databases, tables, and data fields are usually designed, all this data is fairly consistently chronologically ordered. If we want to reconstruct how an international chain of events unfolded, we can usually do that, because most dates are stored as UTC nowadays, or in a format that can be translated into UTC. And the Western dominion over computer systems and standards has led to the fact that the Gregorian calendar and the counting of years as "Common Era" (CE) is far more used than it would be culturally alone. Even the data of people who use, for example, the Islamic calendar, the Jewish calendar, or the Coptic calendar is turned into Gregorian UTC when they post anything on a Western social media platform, use an international bank for transactions, book an international flight, or buy anything on an international online marketplace.
But when did our globally dominant standard year counting actually start? What happened that made a random year into "year 1" for the whole world? And when did people begin dating events using this special counting system over all other previous, well-established systems?
To answer this, we need to understand how the ancient city of Rome fed its citizens, how a short series of unassuming individuals made – from around 30 CE onward – a chain of very unique decisions, each leading to the next, and how finally one ambitious king in Europe around 800 CE standardized our norm of counting the year forever, without ever knowing it.
The grain, the trade route, and two healers
Egypt had grain. The Romans needed bread. That had two consequences. First, the grain had to be transported on ships from Alexandria in Egypt along a long and safe journey along the coast to Italy. Second, this trading route had to be controlled by the Roman Empire to make sure no one could interrupt the trade. Eventually, a Roman puppet king named Herod Antipas ruled one region of Palestine – which lies on this trading route – then called Galilee. At that time, two separate healers in his kingdom gained a lot of popular attention. Herod Antipas had one of them killed, while the other went with a group of his followers north into the kingdom of Herod Antipas' brother, a tolerant man. There, in the villages near the capital – a place called Caesarea Philippi – the second healer could have stayed, healed people, and done as much good as he ever wanted.
But he did not stay there.
His name was Jesus of Nazareth, and he made a strange decision that no historian can explain to this day: he walked all the way south to Jerusalem in Judea, with the sudden intention and precise plan to overthrow the Roman Empire. His plan failed. The Roman prefect in Jerusalem executed Jesus. This inexplicable decision of one man – to try to bring the Roman Empire down – is the root cause of our modern calendar. Yet his action was seen as so unremarkable and common at the time that it left no entry in any history book of that era.
The first written hints
Forty to seventy years later, some people began to write the story down, but they had neither a specific date for Jesus' birth nor his death. Still, one of these authors wrote two crucial hints. He stated that these key events took place in the 15th year of the reign of Emperor Tiberius, and that Jesus was about 30 years old at that time. This was a very common way of dating events, because people back then knew how to count Roman regnal years, but did not need precise historical timelines in daily life.
By the time we reach 100 CE in modern calendar terms, all eyewitnesses were dead. Since then, no one has ever added any new evidence that would help us find a more precise dating of Jesus' life.
Sextus Julius Africanus – the first calculator
Around 200 CE, our next important character entered the stage. He was called Sextus Julius Africanus, and he had access to the text of Luke with its reference to Tiberius and Jesus' age of about 30 years. Sextus Julius Africanus was a well-traveled Roman citizen from Palestine who spent a lot of time in Alexandria and in Rome – the two opposite ends of the grain trading route mentioned above. Based on all the relevant knowledge he gathered, he was able to calculate the birth and death date of Jesus of Nazareth. Of course, there was no concept of our modern year counting back then, so he calculated it in terms of the Roman calendar system. His result was that Jesus must have been born in the 42nd year of Augustus' reign, and that he died in the year of the two consuls Gemini.
But Sextus Julius Africanus was most interested in the age of the entire world. In our modern counting of 221 CE, he defined – based on Jewish scripture and its interpretation – that the universe was 5,500 years old when Jesus was born. Much later, this anno mundi (year of the world) counting nearly became our modern standard.
Diocletian and the stable counting
In the meantime, in 284 CE, Emperor Diocletian started his reign, and as usual the common counting was reset to the "1st year of Diocletian" – as had been done many times with every new emperor. But Diocletian himself then established a rule of four people ruling the vast empire. As a result, the counting was not reset anymore after him. The Diocletian counting became a common standard that stayed long after his death.
Then around 400 CE, a man named Panodorus not only studied the calendar issue intensively in Alexandria (where he lived and had access to the famous library), but also did the heavy work of computing the timespan between the 42nd year of Augustus' reign and the 1st year of Diocletian's reign as 284 years.
Now, following all the years and numbers mentioned so far, at that point in time – around 410 CE – for the first time in recorded history, the birth of Jesus was reliably anchored to an absolute, well-established common calendar. Not only was Jesus placed at "284 before Diocletian", but also every date that could be expressed in the Diocletian counting became identifiable as Diocletian plus 284 years since the birth of Jesus. Still, no one began to use any dating method from this new angle – our modern angle.
The collapse of Rome and a monk named Dionysius
Then the Roman Empire in the West – in Rome itself – collapsed as a political power. In the aftermath, the bishops of Rome, still part of an international network of Christian communities, one after another walked into the political vacuum in the West. This brings us, in an astonishing turn of events, to a monk named Dionysius Exiguus, a Greco-Roman from the East who eventually worked for a series of bishops in Rome over decades. One day around 525 CE, he received a task: to provide new so-called Easter tables. He started with the existing ones, which would run out soon, and added a new extension – something like a modern Excel sheet.
But this monk did not like Diocletian. (Diocletian had been a fierce persecutor of Christians.) Therefore, in a fascinating turn of events, he decided to rearrange the "year" column of the table. He copied the old one, added the new years as new rows, and recomputed the Diocletian years into years since Jesus' birth. He renamed the header of the column Anno Domini – "the year of the Lord". Then he even sent the table to a monk in the East as an attachment to a letter. And this letter, written in 525 CE, he dated as 525 Anno Domini. It is the first letter in the history of humanity that was dated using our modern counting of years.
Then Dionysius died, and with him the whole new idea died.
The Venerable Bede – the unexplained switch
It took another 200 years for the idea to resurface. Some Anglo-Saxons had moved over into Britain, merged with the existing people there, and had become Christians. They built monasteries and by that joined the international network of "the Church". An ambitious example of a new monastery was built in Northumbria, and there another monk gained access to a very modern library filled with copies of books – especially from Alexandria, Eastern Rome, and Rome itself.
Around 700 CE, this new character entered the stage: the Venerable Bede. He, in this chain of events, made a crucial decision that no one can explain. He spent decades studying, describing, and fiercely debating how to correctly calculate the age of the universe. As a result, in 725 CE he published an encyclopedia explaining in depth why the world – the universe – must be exactly 3,952 years old. He also added a history of the world in which he dated all events based on this calculation of anno mundi.
But then, surprisingly, from 726 CE to 731 CE he wrote another book covering the history of the Anglo-Saxons from a Christian perspective. In this book, without any explanation, he suddenly dated all events in the Anno Domini counting – the years since Jesus' birth. It became the first book that ever dated events in our modern CE reference.
Why did he change his mind? He left a lot of texts, but in none of them does he explain his switch from being a fanatical defender of an anno mundi system – spending decades of work on it – to using Anno Domini counting from one book to the next. This remains an unsolved mystery in the history of the calendar.
Side note: At this point, the Islamic expansion had reached its largest geographical and political extent, from India to France. That empire had its own calendar. It started with year one in modern 622 CE, and was already a common standard for a vast part of the world.
Charlemagne, Alcuin, and standardization
Bede's book became niche-popular, but again nothing much happened to popularize the new counting of years going back to Jesus. In the same century, an ambitious king of the Franks met a later monk from Northumbria – a student of Bede's works. This monk, named Alcuin, became the king's advisor and helped him become Charlemagne, the Holy Roman Emperor. Eventually, they established a new Roman Empire in the West, with a pope in Rome, a political center in Aachen, a mixture of people with all sorts of inheritances in a new European order, and a church centered in Rome as the border‑crossing glue of a very fluid European political scene.
Alcuin helped Charlemagne set standards – a common currency, for example – and also the Anno Domini date. But again the effect and spread were rather slow. The first inscription on a building in the AD format can be found on the facade of the Cathedral of Pisa. It reads: Anno Dominicae Incarnationis M. LXIII – "In the year of the Lord's Incarnation 1063".
From Roman numerals to global standard
Around 1190 CE, a man from Pisa became consul in Algeria, and his son learned the Arabic numerals there. He became famous as Fibonacci, and with him Western culture changed to expressing years as "1063" instead of "MLXIII". (It remains a peculiar tradition that at the end of movie credits, the year is often still expressed in Latin form, so 2026 is shown as MMXXVI.)
Around 1450 CE, the printing press began to have its effect. Anno Domini dates in texts were copied and distributed en masse. Our modern understanding of the year became the norm in the West. The copyright notice – literally present in every single publication – uses this year.
From Anno Domini to Common Era: the Kepler transition
But there were two more twists to come. Yes, the Gregorian calendar reform happened in 1582 CE – that changed the structure of the calendar but did not change the year itself.
The first new twist came in 1615 CE, when an astronomer named Johannes Kepler published a book in which he called the year annus aerae nostrae vulgaris – "year of our common era". This phrase was later translated into English as "Common Era", now abbreviated as CE. Kepler demonstrated that the reference of counting years from Jesus' birth had evolved from something uniquely Christian into something completely common – a civil standard now used by believers and non‑believers alike.
This was the intellectual bridge: AD remained the ecclesiastical term, while CE became the inclusive, global, secular equivalent. Today, databases, logs, and international standards use CE precisely because of this shift that Kepler articulated.
As we know, the system could have ended in 2000 CE when the so‑called "Y2K bug" caused a lot of headaches. And – if computers and databases stay in their core the same until the year 9999 – the whole CE system will face another crisis on the 1st of January, 10000.
The chain of decisions
Overall, the chain of decisions is traceable: from Jesus of Nazareth in the villages of Caesarea Philippi, to Dionysius extending an Easter table in Rome, to Bede writing a history book in Northumbria, to Alcuin helping Charlemagne in Aachen to standardize a new Holy Roman Empire in Europe. The individual decisions on that journey are more or less mysterious, but the result is global and now deeply baked into humanity.
The year on your screen right now – 2026 – exists because a healer made an inexplicable decision to walk south, a monk disliked a dead emperor, a scholar switched calendars without explanation, and a king needed a standard.
And that is what year it is.
Timeline of key decisions
- ~30 CE – Jesus walks to Jerusalem
- ~200 CE – Africanus calculates birth in Roman terms
- 284 CE – Diocletian's reign starts
- 525 CE – Dionysius writes first Anno Domini letter
- 731 CE – Bede switches to AD without explanation
- ~800 CE – Charlemagne and Alcuin standardize AD
- 1190 CE – Fibonacci introduces Arabic numerals
- 1450 CE – Printing press mass‑distributes AD dates
- 1615 CE – Kepler coins "Common Era"
First published on dev.to. This article is CC BY‑NC 4.0.
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