Calendars: From Roman to Gregorian and Beyond

Isn’t the history of the calendar oh so very simple and… oh… no? Well, I hope I break this down for you then.

An early Roman calendar

Roman Calendars (509 – 45 BC)

Unfortunately, it’s not as easy as saying ‘there’s a roman calendar and here are the dates when it was used’, there are many versions of Roman calendars, which I will try and list as concisely as possible below. The earliest Roman calendar was probably some kind of lunar calendar, based on the shape of the moon (each month starting at the first crescent moon and lasting 29 – 30 days). Early Rome had an 8 day week, so this was probably also part of the early calendar.

The 10 Month Calendar

The first organised Roman calendar was a 10 month cycle of 30 – 31 days each. The year began with the Month of Mars, followed by the Month of Apru, the Month of Maia, the Month of Juno, then the fifth, sixth, seventh, eighth, ninth and tenth months. This system added up to 304 days, leaving 50-60 days as an “unorganised winter”. But there are other theories that say that these days were inserted into months until the calendar lined up nicely with the seasons once more.

Some credit Romulus himself with the creation of the 10 month calendar, but as we know (if you’ve listened to Have You Ever Heard Of…?‘s Romulus episode), Romulus’ story isn’t exactly grounded in solid fact.

The Republican Calendar

According to one source, the Roman calendar changed again in 154 BC, adding January and February as winter months. It followed Greek calendars in assuming a lunar cycle of ​29.5 days and a solar year of ​12.5 months (​368 3⁄4 days), which align every fourth year (a bit like a leap year). The calendar followed a four year cycle of 355 days, 376 days, 355 days and 377 days. Each month had between 27 – 31 days in with March, May, July and October having 31.

Julius Caesar

The Julian Calendar (45 BC – 1582)

In 45 BC a new calendar came into being, at the behest of Julius Caesar – it was designed with the help of Greek mathematicians and astronomers. The Julian calendar was used in most of Europe, and other parts of the Roman world, for 1,600 years. Lengths of the months are identical to what we follow now and a leap year in February was established every four years.

Greek mathematician Eudoxus (c. 408 – c. 355 BC) is popularly credited with having determined the length of the year to be ​365 1⁄4 days, but his works are lost.

However, a typical solar year is actually very slightly shorter than 365 1/4 days (365.24217 days) and because of this the calendar year gains about 3 days every four centuries. So…

The Astrological Clock in Prague

The Gregorian Calendar (1582 – Present)

Mostly, around the world, we now use the Gregorian Calendar.

Adoption in Europe

Adopted first in 1582 by Catholic states such as France, Italy, Poland-Lithuania, Spain and Portugal (as well as the Catholic states of the Holy Roman Empire), Thursday 4th October 1582 was followed by Friday 15th October 1582. This skipped ten days and helped level out the slippage from the Julian calendar.

Adoption in protestant countries took a little longer. Some saw it is a Catholic invention and didn’t want to take part. Queen Elizabeth, for example, was talked out of it. Britain and her Empire (including the USA) adopted the Gregorian Calendar in 1752. Wednesday 2nd September 1752 was followed by Thursday 14th of September, as they were now 11 days behind. Interesting, Britain moved New Year’s Day to 1st January at the same time, rather than 25th March.

Other European countries adopted the Gregorian calendar along the way. Prussia in 1612, Denmark and Norway in 1700, Sweden (after some weird and wonderful calendar madness) in 1753 and not until 1916 did Bulgaria join. Russia joined during the October revolution and in 1918 they dropped 13 days from February (31st January was followed by 14th February). Others who were late to the party, mostly Eastern Orthodox countries, were Romania (1919), Greece (1922) and Turkey (1926).

Adoption in Asia

Japan had been following a traditional lunisolar calendar since the sixth century, and joined the Gregorian calendar and the end of 1872. Japan uses traditional Japanese names for the months, e.g. 八月 (hachigatsu) for August, which means the ‘Month of Leaves’. They also name their years after eras, currently we are in Reiwa, which began on 1 May 2019.

Korea followed in 1895, but during some periods used different names for the years. For example, between 1948 – 1962 Korean era names were used.

North Korea, from 1997, counts years based on the Juche era, which began in 1912, so the current year in North Korea is Juche 110, which still correlates to Gregorian 2021. In North Korea all years before Juche 1 are labelled using Gregorian numbers, so it went 1910, 1911, Juche 1. Interesting place, DNK.

China adopted the Gregorian calendar at the start of 1912 but because of warlord fighting, with different warlords using different calendars, it got confusing. Under unification in 1928 the Nationalist government stated all should use the same calendar from 1929. China retain Chinese numbering for months but use Western numbered years. Interestingly, Taiwan still use the Republic of China’s era system for their years (year one being 1912).

Alongside Calendars

Some countries use both the Georgian calendar in conjunction with another.

Some countries, such as Saudi Arabia, use the Gregorian calendar (adopted in 2016) for civil and political purposes and the Islamic calendar for religious ones. Pakistan also uses this method too. The Islamic calendar is a lunar one with 12 months and 352/355 days in a year (11 days shorter than a solar one).

India, Bangladesh, Israel and Myanmar all also use other calendars in conjunction e.g. the Hebrew calendar in Isreal.

Countries Who Don’t Use Gregorian

Although most countries use the Gregorian calendar in some capacity, some countries don’t use it at all. Those that don’t are: Ethiopia, Nepal, Iran and Afghanistan.

The Persian Calendar, used in Iran


Why does this shift in calendars cause problems for us? Well, lets take an example. King George II was born on 9 November 1683 so on 9 November 1752 he would have turned 69. Except actually he would have been 11 days short of 69… and what about the people born in the skipped days? (2th – 14th September in England) Did they celebrate on the 14th and then revert back to their original date the next year?

Additionally, when it began there were some issues because certain countries had switched and others hadn’t. For example Napoleon’s victory at the Battle of Austerlitz in 1805 may have been partly down to the fact that the Russians were using the Julian calendar and the Austrians the Greogian, so they messed up getting their armies together.

And this brings us to the biggest problem for historians. Lets say we’re writing a book about what different countries were doing on 16th August (MY BIRTHDAY) 1700. If we wanted to be exact we’d have to make a list of which countries had adopted the calendar by 1700 and which hadn’t, then aline them correctly. Also, a number of countries, Russia included, were still behind during World War One, and some even during the second. IN FACT, at the time of writing this it’s 8 January 2021, UK calendar but in Iran it’s 19 Dey 1399. I’m not by ANY MEANS saying our way of doing this is the “correct” way, just that it takes leg work to get all the ducks in line.


So, is the Gregorian calendar really the best one we could have? Some say no. Why? Well, one reason is because of the 365 days in a year and 7 day a week balance, there’s no easy way of telling what day of the week any given day would me. It’s not like every 1 January is a Monday, for example. One way of solving this would be to use something called the World Calendar. In this the year would be 364 days, starting on a Sunday, and then the 365th day would be called “world day” and the 366th, when it occurs, would be “leap day”. Personally, I’m not a fan of this system. Think about it, it’s nice to sometimes have your birthday on a weekend! Other calendars want to solve this by having either 364 days or 371 days, depending, thus solving the problem, which to me, doesn’t seem like such a big issue.

Others wish to even out the months by making 13 months of 28 days. There is an issue with this, in that it only equates to 364 days. A man named James A. Colligan invented something called the Pax Calendar in 1930 that adds a “leap week” in between month 12 (now Columbus) and December, when needed.

There are other alternative calendars and perhaps more reforms will happen in the future, but for this historian, I’m glad I mainly think about the past and don’t have to think about that too much.

Posted by

Writing about things!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s