When did we start counting years in our current calendar? Did Jesus die and people just said “ok we are now in 33AD and there will be 12 sections every year, each with around 30 days”.
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People have been counting years in calendars long before Jesus. It was typically measured by whomever the reigning leader was – i.e. the 7th year of the reign of King Bob.
The modern calendar was created by the Catholic Church in the 5th century to better predict when Easter would be (as Easter is based on the lunar calendar rather than a fixed day of the year). Naturally, they used the birth of Christ as the starting point of this new calendar, and as the Catholic Church was very powerful, their calendar became the dominant one.
The individual months are based on the Roman calendar, tweaked over many centuries.
Those things all came around at different times.
The oldest calendars are lunar calendars – the moon orbits the earth 12 times a year, plus a few straggler days that make every lunar calendar a disaster. Calendars have had “moonths” for as long as we’ve been writing about it.
The ancients eventually noticed that the solar year isn’t 365 days long either, it’s a frustrating 365.2425 days long and so you need to add leap days in occasionally to stop drift. The Romans put this into place two thousand years ago.
Setting the birth of Jesus as year zero didn’t come around until the 6th century. The church got tired of trying to synchronize calendars between different kingdoms with their own zero date based on local rulers and dynasties, and so they worked backwards to try and calculate when Jesus was probably born to set a global year zero for all church records.
They’re probably actually off by a few years, but they got pretty close considering the source documents they had to work with.
The Julian calendar was proposed in 46 BC by Julius Caesar, and named that because he wasn’t very humble. It took effect on 1 January 45 BC, by his edict. In 1582 Pope Gregory XIII promulgated a revised calendar, the one we use today, also very humbly named the Gregorian Calendar. Jesus and the folks who lived in his era were all using the Julian calendar.
The Gregorian calendar is, to some extent, based on a hodgepodge of earlier systems. The idea of dividing the year into 12 months of around 30 days each was actually rather new at the time Jesus was born, having been proposed by Julius Caesar and later modified by the emperor Augustus. Before then the Romans had used a 10-month calendar, which is why the names of the last few months of the year derive from the numbers 7, 8, 9, and 10 even though they’re the 9th, 10th, 11th, and 12th months.
But that calendar still counted its years from the founding of Rome, or *AUC* *(ab urbe condita)*. Switching over to the supposed year of Jesus’s birth didn’t happen until the year that we now call AD 525. Before then Christians had been counting from year that the emperor Diocletian, the last emperor to institute major persecution against Christians, began reigning (AM, *anno martyrium*). A monk named Dionysius Exiguus was working out a new system for calculating the date of Easter, and introduced the idea of calculating from the years since Jesus’s birth in order to stop celebrating the faith’s persecution. This caught on quickly, even though Dionysius’s calculations for Jesus’s birth are now thought to have been a few years off. This is one of the reasons you sometimes see the same era referred to as *CE* (Common Era): if Jesus wasn’t born that year anyway, then it makes little sense for the calendar to say that he was.
But in any event, Dionysius’s reform wouldn’t be the last. The Julian Calendar is responsible for the famous leap-year rule of adding an extra day to February every four years. the problem with this is that it’s actually too frequent: Earth takes very slightly longer to go around the Sun than this. The margin of error is about 3 days every 400 years. This doesn’t seem like a lit, but by 1582 the calendar had drifted out of alignment by almost two weeks, and people began to notice. One important function of the calendar was to track the seasons, and people didn’t want it drifting too far out from the typical norms. So a new calendar was proposed, almost identical but with a different leap year rule. This is the *Gregorian calendar*. In this calendar leap years happen every four years, except when the year was divisible by 100, *except* when the year is divisible by 400 (so 2000 was a leap year but 1900 was not and 2100 won’t be). This gets us much closer to the proper targetfor keeping things on track. There’s still a small margin of error, but it will take thousands of years before the calendar even drifts by a day.
And that’s the answer to your question. Our current calendar was built up slowly over time, rarher than suddenly shifting to what we now know.
There was a British monk named Bede in the 700s AD who calculated Jesus’ birth year and created the AD/BC system. Fun fact, he goofed up and that’s why Jesus is now listed as born between 4 BC and 2 BC.
Before that see the most common calendar in Europe used AUC, which pit its 0 year at the founding of the city of Rome
The Roman Calendar was based on the lunar cycle which is 29.5 days, and so for that reason the calendar was alternating between 30 and 31 days. The Roman Calendar was also only 10 month long so December was the 10th month of the year since Dec is the suffix for 10 in Latin.
The rest of the year was just winter, people were mostly staying inside, there was no war, no agriculture, etc so keeping track of the days wasn’t really a priority. Later as administration become more important, they added the month of January and February as the months of winter. The Lunar year is 355 days while the Solar year is 365 and a quarter, when they didn’t count the months of winter it didn’t really matter, but since they started doing it, it became an issue. They was a lot of weird experimentation with the calendar, January and February had 28 days, another time the 30 days months become 29 days, etc. Then in 46 BC Julius Cesar reformed the calendar to the structure we have today with 12 months of 30, 31 days and a leap day each 4 years.
Some minor changes still occurred after that like changing the month of Quintillis to July in honor of Julius Ceasar, or the month Sextillis renamed August in honor of Augustus. The Starting year of the Roman Calendar was the founding of Rome, but later the Byzantines used the same calendar but starting from ”the Creating of the World” which was in 5509/08 BC according to them. During the Roman Calendar, the week was 8 days, but after the Julian Calendar the 7 week started to be used until it became law under Emperor Constantine.
Oh no. Anno Domini notation came about in AD525, invented by a monk, one called Dionysius the Humble, who back calculated easters to supposed birth of Jesus. It wasn’t until second millennium that the system actually became widely used.
It’s much like the Jewish Anno Mundi, calendar supposedly counting years from the creation of the Earth(an entirely fictional event), they are at year 5784 right now. Of course they didn’t start counting six thousand years ago, modern form of that calendar wasn’t reached until 10th century.
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