A page from the "Calendars" exhibit...

History of Our Calendar

Pope Gregory XIII. Portrait by Lavinia Fontana

Pope Gregory XIII dedicated his papacy to implementing the recommendations of the Council of Trent. By the time he reformed the Julian calendar in 1582 (using the observations of Christopher Clavius and Johannes Kepler), it had drifted 10 days off course. To this day, most of the world uses his Gregorian calendar.

Before today’s Gregorian calendar was adopted, the older Julian calendar was used. It was admirably close to the actual length of the year, as it turns out, but the Julian calendar was not so perfect that it didn’t slowly shift off track over the following centuries. But, hundreds of years later, monks were the only ones with any free time for scholarly pursuits – and they were discouraged from thinking about the matter of "secular time" for any reason beyond figuring out when to observe Easter. In the Middle Ages, the study of the measure of time was first viewed as prying too deeply into God’s own affairs – and later thought of as a lowly, mechanical study, unworthy of serious contemplation.

As a result, it wasn’t until 1582, by which time Caesar’s calendar had drifted a full 10 days off course, that Pope Gregory XIII (1502 - 1585) finally reformed the Julian calendar. Ironically, by the time the Catholic church buckled under the weight of the scientific reasoning that pointed out the error, it had lost much of its power to implement the fix. Protestant tract writers responded to Gregory’s calendar by calling him the "Roman Antichrist" and claiming that its real purpose was to keep true Christians from worshiping on the correct days. The "new" calendar, as we know it today, was not adopted uniformly across Europe until well into the 18th century.

Here are a few more historical aspects of our calendar.

Has the year always started on 1 January?

In some ways, yes. When Julius Caesar introduced his calendar in 45 B.C.E., he made 1 January the start of the year, and it was always the date on which the Solar Number and the Golden Number were incremented.

However, the church didn’t like the wild parties that took place at the start of the new year, and in C.E. 567 the council of Tours declared that having the year start on 1 January was an ancient mistake that should be abolished.

Through the middle ages various New Year dates were used. If an ancient document refers to year X, it may mean any of 7 different periods in our present system:

1 Mar X to 28/29 Feb X+1
1 Jan X to 31 Dec X
1 Jan X-1 to 31 Dec X-1
25 Mar X-1 to 24 Mar X
25 Mar X to 24 Mar X+1
Saturday before Easter X to Friday before Easter X+1
25 Dec X-1 to 24 Dec X

Choosing the right interpretation of a year number is difficult, so much more as one country might use different systems for religious and civil needs.

The Byzantine Empire used a year starting on 1 Sep, but they didn’t count years since the birth of Christ, instead they counted years since the creation of the world which they dated to 1 September 5509 B.C.E.

Since about 1600 most countries have used 1 January as the first day of the year. Italy and England, however, did not make 1 January official until around 1750.

In England (but not Scotland) three different years were used:

The historical year, which started on 1 January.

The liturgical year, which started on the first Sunday in advent.

The civil year, which

from the 7th to the 12th century started on 25 December,
from the 12th century until 1751 started on 25 March,
from 1752 started on 1 January.

→ See the British Calendar Act of 1751.

It is sometimes claimed that having the year start on 1 January was part of the Gregorian calendar reform. This is not true. This myth has probably started because in 1752 England moved the start of the year to 1 January and also changed to the Gregorian calendar. But in most other countries the two events were not related. Scotland, for example, changed to the Gregorian calendar together with England in 1752, but they moved the start of the year to 1 January in 1600.

Then what about leap years?

If the year started on, for example, 1 March, two months later than our present year, when was the leap day inserted?

When it comes to determining if a year is a leap year, since AD 8 the Julian calendar has always had 48 months between two leap days. So, in a country using a year starting on 1 March, 1439 would have been a leap year, because their February 1439 would correspond to February 1440 in the January-based reckoning.

What is the origin of the names of the months?

A lot of languages, including English, use month names based on Latin. Their meaning is listed below. However, some languages (Czech and Polish, for example) use quite different names.

JanuaryJanuariusNamed after the god Janus.
FebruaryFebruariusNamed after Februa, the purification festival.
MarchMartiusNamed after the god Mars.
AprilAprilisNamed either after the goddess Aphrodite or the Latin word aperire, to open.
MayMaiusProbably named after the goddess Maia.
JuneJuniusProbably named after the goddess Juno.
JulyJuliusNamed after Julius Caesar in 44 B.C.E. Prior to that time its name was Quintilis from the word quintus, fifth, because it was the 5th month in the old Roman calendar.
AugustAugustusNamed after emperor Augustus in 8 B.C.E. Prior to that time the name was Sextilis from the word sextus, sixth, because it was the 6th month in the old Roman calendar.
SeptemberSeptemberFrom the word septem, seven, because it was the 7th month in the old Roman calendar.
OctoberOctoberFrom the word octo, eight, because it was the 8th month in the old Roman calendar.
NovemberNovemberFrom the word novem, nine, because it was the 9th month in the old Roman calendar.
DecemberDecemberFrom the word decem, ten, because it was the 10th month in the old Roman calendar.

How did Dionysius date Christ’s birth?

There are quite a few theories about this. And many of the theories are presented as if they were indisputable historical fact. The following are two theories that tend to be more accepted:

According to the Gospel of Luke (3:1 & 3:23) Jesus was "about thirty years old" shortly after "the fifteenth year of the reign of Tiberius Caesar." Tiberius became emperor in C.E. 14. If you combine these numbers you reach a birthyear for Jesus that is strikingly close to the beginning of our year reckoning. This may have been the basis for Dionysius’ calculations.

Dionysius’ original task was to calculate an Easter table. In the Julian calendar, the dates for Easter repeat every 532 years. The first year in Dionysius’ Easter tables is C.E. 532. Is it a coincidence that the number 532 appears twice here? Or did Dionysius perhaps fix Jesus’ birthyear so that his own Easter tables would start exactly at the beginning of the second Easter cycle after Jesus’ birth?

Was Jesus born in the year 0?


There are two reasons for this:

There is no year 0.

Jesus was born before 4 B.C.E.

The concept of a year "zero" is a modern myth (but a very popular one). In our calendar, C.E. 1 follows immediately after 1 B.C.E. with no intervening year zero. So a person who was born in 10 B.C.E. and died in C.E. 10, would have died at the age of 19, not 20.

Furthermore, as described in section 2.14, our year reckoning was established by Dionysius Exiguus in the 6th century. Dionysius let the year C.E. 1 start one week after what he believed to be Jesus’ birthday. But Dionysius’ calculations were wrong. The Gospel of Matthew tells us that Jesus was born under the reign of king Herod the Great, who died in 4 B.C.E.. It is likely that Jesus was actually born around 7 B.C.E.. The date of his birth is unknown; it may or may not be 25 December.

Why do the 9th thru 12th months have names that mean 7th, 8th, 9th and 10th?

September through December were the seventh through tenth months of a calendar used by the first Romans. Ancient historian and Greek biographer Plutarch, wrote in C.E. 75, about how they became displaced to two positions higher than their names would indicate.

Read excerpt of Plutarch’s essay.

Read more about the early Roman calendar.

Why does February have only 28 days?

January and February both date from about the time of Rome’s founding. They were added to a calendar that had been divided into ten month-like periods whose lengths varied from 20 to 35 or more days. A winter season was not included, so those period lengths are believed to have been intended to reflect growth stages of crops and cattle.

When introduced, January was given 29 days and put at the beginning of the calendar year. February was given 23 days and put at the end. Then, for an undetermined period shortly after Rome’s founding, months were said to have begun when a new moon was first sighted. At some later time, month lengths were separated from lunations and again became fixed. At that time, February’s original length was extended by five days which gave it a total of 28.