Star of Bethlehem IV: Why do we celebrate Christmas on December 25?

Why do we celebrate Christmas in December? It is actually a long and quite complicated story. Most people do not realise that the date that we celebrate Christmas Day now is not the same as it was in times of Christopher Columbus. Similarly, they do not realise that many of our Christmas traditions were imported from Germany in the 19th Century, but reproduce closely a pagan festival that was old even in Roman times.

We have seen how the Moon provides, in the form of an eclipse, a major clue about the date of the Nativity. There is a big astronomical connection, again involving the Moon, in how the modern calendar was set.

It is often said that Charles Dickens rescued Christmas. He popularised the celebration in his novels at a time when its celebration was becoming increasingly unimportant. However, traditions such as the Christmas tree, which is obligatory in almost every house now, were popularised by Prince Albert, husband of Queen Victoria. Albert missed many of the traditions of his country when he went to live in London and  introduced them in the British royal family; the population imitated the celebrations of Victoria and Albert and now these traditions have spread around the world.

What do we associate with Christmas?

  • A religious celebration
  • The most important public holiday of the year.
  • Parades in the streets.
  • Giving and receiving of gifts.
  • Special meals and feasts.
  • Decorating houses with green bows.

Actually, these were the ways that the festival of Sol Invictus, or Saturnalia (the festival of  Saturn) were celebrated. It was the most important festivity in Rome, marking the shortest day of the year and had been celebrated by the Celts even before the Romans from at least 1000BC. Therefore, rather than abolish a popular holiday, the traditional view (although challenged in recent decades by revisionists) is that the early Christian church adopted it and adapted it as their own second most important celebration.


Over the centuries the religious aspects of Christmas have taken a back seat leaving a celebration that would feel familiar to a Roman from the time of Julius Caesar: drop a Roman into a modern Christmas and he would very much at home in many ways. Religious celebration on December 16th; giving and receiving of presents on the 19th – Sigliaria, a day when children received toys and adults could receive anything from a token clay ornament from an acquaintance to a slave from a very close friend; and a lot of eating, drinking and noisy celebration.

What do we know about the formal origins of December 25th as Christmas Day?

The transformation of December 25th seems to have started with the decree of Emperor Aurelius in 274 AD. After fifty years without celebrating the cult of the Sun he set this day as the celebration of Sol Invictus. The date became so important that in one of his Christmas sermons, Augustine of Hippo (St Augustine, 354-430 AD) declared:

We celebrate this day as a holiday, not in the name of the Sun, worshiped by its believers as much as by us, but in the name of he who created the Sun.

The calendar of Filocalus, also known as the Chronography of 354, contains what seems to be the first written reference to Christmas as a holiday. While it refers to December 25th as the celebration of “Natalis Invicti” (Sol Invictus), in Chapter 12 we find the dates of the celebration of the martyrs, starting with:

VIII kal. Ian, natus Christus in Betleem Iudeae

(Eighth day before the Kalends of January (December 25th), birth of Christ in Bethlehem, Judea)

Although we know that Christians celebrated December 25th before the 4th Century, it was a celebration that was accepted only gradually as the early church had a belief that the celebration of birthdays was a sin. Origen of Alexandria (184/185-253/254), theologist and early Christian philosopher wrote, based on Old Testament beliefs, that

Only a sinner celebrates his own birthday

The extension of this belief between Christians that celebrating a birthday was a pagan practice makes us believe that until the mid-3rd Century Christmas Day was not celebrated, even though Epiphany was. Some authors believe that the celebration of Christmas began to gain ground in the 3rd Century as an alternative to the existing pagan practices.

What we know for certain is that from 221 AD Sextus Julius Africanus (c. 160 – c. 240) popularised December 25th as the date of birth of Jesus through his work “The Chronicle”, published in Greek as Χρονογαφιαι “Chronographiai”. We know that the Council of Nicea in 325 AD debated the dates of Christmas and Epiphany, but that by then the Alexandrian church had fixed “Díes nativitatis et epifaníae” and the dates seemed to be fairly widely accepted, if not celebrated. Certainly we know that Dionisius Exiguus set out a reasoning for Christmas Day being December 25th based on Jesus’s life story and, by then Christmas was an established part of the Christian calendar.

In between these first references and Dionisius we know that Emperor Constantine I, although a Christian, was also a great admirer of the Sun and decreed that dies solis – the Day of the Sun – should henceforth be a day of rest. As recently as the reign of Diocletian, twenty thousand Christians had been put to death between 303 and 311 AD. One of the first acts of Constantine on becoming recognised as emperor in both the eastern and western empire was the Edict of Milan, introducing religious tolerance and ending this persecution.

In a world in which Christians had been distrusted and often persecuted for centuries, getting the average Roman to accept Christian beliefs suddenly would have been the hardest of hard sells however, by making dies solis the Christian Sunday and Sol Invictus, Christmas, the change was sweetened. It is like a wonderful scene in the film “Chariots of Fire”:

We remember how a boy, who was playing football outside the church, runs into Eric Liddle when he was leaving it after the Sunday service. Eric reproaches him for his lack of respect for the Sabbath and offers to play him before work on Monday instead. When Eric’s friends question this, Eric responds “do you want him to grow up thinking that God’s a spoilsport?”

As Augustine of Hippo pointed out, pagans would keep their favourite celebrations and, slowly, would become accustomed to the Christian celebration both of Sunday and of Christmas. This was typical of the way that the early church christianised pagan practices.

The Changing date of Christmas

Have we always celebrated Christmas on December 25th since Roman times? Not quite!

Actually, it is a matter of definition. In 1582, Pope Gregory emitted a Papal Bull to correct the Julian calendar that had been set up on the advice of Sosigenes by Julius Caesar in 45 BC. The Julian calendar, as it became known, was a massive improvement on the rather arbitrary system of leap months that existed previously. It was the duty of the Pontifex Maximus to decide whether or not to add a leap month to a particular year. However, as the political offices of magistrate ran from January 1st to December 31st, it became the practice that if the magistrates were not to the liking of the Pontifex, their term of office would be shortened by skipping the need for the leap month that should have been added about every third year. Over the years the calendar started to slip badly: by 46 BC it was two months out of phase.

The pre-Julian year of 355 days (a lunar year), became a year of 365 days with a leap day every fourth year. It allowed Pliny to calculate, a century later, that the solstice happened on December 25th (that date, again!) However, Sosigenes was either unaware, or simply unconcerned that a solar year—the period of revolution of the Earth around the Sun—is not 365.25 days but, in fact, 11m14s less. Hence, we add too many leap days, and the Julian calendar slips too, if only slowly: we lose a day every 128 years.

Pope Gregory’s Bull, “Inter gravissimas” corrected the slip in the calendar that, by 1582 had reached 10 days, by jumping straight from Thursday October 4th 1582 to Friday October 11th 1582 and, additionally, decreeing that century years would only be Leap Years if divisible by 400 such that 1900 was not a Leap Year, but 2000, yes [1].

Apart from the fact that the Bull only applied to Catholic countries so, for instance, it was ignored in protestant countries such as England and Wales and Germany, but also in countries such as Greece and Russia that followed the Orthodox Church. There was a religious rebellion as some Christians objected to the date of Christmas effectively becoming ten days earlier after calendar reform. For decades many Christians celebrated Christmas Day on January 4th, which was its date in the old Julian calendar.

Effectively, relative to solar time, Christmas had been celebrated one day later every 128 years and, in non-Catholic countries, would continue to be until they adopted the Gregorian calendar. One of the strange consequences is that Christmas Day is, in fact, celebrated three times in Bethlehem:

  • Catholics and protestants celebrate Christmas on December 25th,
  • Greeks, Syrians, Russians and other followers of Orthodox churches celebrate Christmas on January 7th[2], and
  • The Armenian Orthodox Church celebrates Christmas on January 18th, the day of Epiphany.

Was the Nativity really in December?

Dionisius Exiguus followed church dogma by stating that Jesus died on March 25th, at the age of 33 years and 3 months, hence the Nativity took place on December 25th. Do we actually have any evidence of this?

For decades people have repeated without question: certainly not!  The reasoning being that shepherds would not have been watching their flocks by night, except at lambing time. And therefore, the presence of shepherds watching their flocks by night suggested that the Nativity took place in March, April, or early May. The cold and humid weather of December and January would be an invitation to pneumonia for shepherds who spent the night out in the open.

I started to doubt this assertion because it is based on practice in the British Isles, so I wondered if lambing time might not be earlier (or later) in Judea.  In fact, even in the British Isles lambing time can vary by several months according to the race of sheep.

The United Nation Food and Agriculture Agency reports state that, in 2013, there were over a million sheep and goats in Palestine and that they have a typical gestation period of five months. Furthermore, they state that for five thousand years the typical breed of sheep in Palestine has been the Awassi. Hence, modern practices are strongly indicative of practices in biblical times.

Lambing time for the Awassi depends critically on having sufficient pasture for the ewes to allow them to fatten before giving birth. Lebanon, Syria and Israel have a Mediterranean climate with a distinct rainy season that starts in October. January is the wettest month and the rains have effectively ended in April.

Bethlehem rainfall
Average rainfall in Bethlehem over the year

The ewes gain weight and strength with the new grass that grows with the first rains of October, losing weight as the dry season progresses and they are obliged to eat increasingly drier grass. Lambing time for the Awassi is December and January. Would shepherds have been in the fields at night then? The answer still is: certainly not! Here’s why.

Conditions on the Castellan plains in the northern third of the Iberian Peninsula are not very different to those around modern Bethlehem. As part of my research I spoke to shepherds on those plains who told me that they would have their animals either under cover, or drive them to lower altitudes in winter; they would sleep out with their flocks between March and September, particularly if large predators were present. We know that this is and was the practice too around Bethlehem where the landscape is dotted with natural limestone caves such as this one shown below that are used by shepherds as natural shelters in winter.

Natural limestone cave (above and below ground) where shepherds take shelter with their flocks at night.

The animals graze outside during the day and are driven in at night to sleep under shelter. But maybe the climate different though in biblical times?

Well, it is well known that the Roman Empire flourished during an unprecedented warm epoch. At the times of the greatest northward expansion of the Roman Empire, temperatures were significantly higher even than now (by about 1°C on average), particularly between 21 AD and 50 AD. The image of Roman legionaries shivering on Hadrian’s Wall, at the northern limit of the empire is somewhat of an exaggeration[3].

The paleoclimate can be determined from the O16:O18 ratio in hydrated minerals in caves and from tree rings. We know from study of the cave at Soreq, west of Bethlehem, that the climate of Judea was significantly more humid two thousand years ago, a fact that Josephus alludes to when he states of Judea that “both its nature and its beauty are a marvel; its soil so fertile that all types of tree grow there”. The region was particularly humid and fertile between 1000 BC and 700 BC. We also know that a major deforestation started around the time of the Jewish revolt in 67-70 AD.

What we can conclude is that—at the time of the Nativity—Judea was warmer, wetter, and considerably more fertile than it is today. While the shepherds would have appreciated the warmer weather, the corollary is that climate extremes would likely have been greater than now, and the higher humidity would have made winters even less pleasant for the shepherds than it is now.

Shepherds would have slept out with their flocks in spring and summer to guard against predators. Even foxes are a danger to new born lambs and, in Roman times, the fauna of the Mediterranean was very different than it is now. For example, today there are around two thousand wolves in Spain and some bears around the Pyrenees. In the whole of Syria, Lebanon, Israel and Jordan it is estimated that only about six hundred wolves remain. In Roman times though, wolves would have been the least of the shepherd’s problems as elephants and bears roamed the whole of North Africa, while the Atlas Lion ranged from Morocco in the west to Pakistan in the east. Quite apart from wolves, a shepherd in Bethlehem might need to scare off a mother bear with her cubs, or a hungry lion looking for an easy meal.

In conclusion, the fact that shepherds were watching their flocks does little to limit the range of dates. We can only say that it strongly suggests we should exclude the months of November, December and January, which means that the Nativity certainly did not happen on December 25th, but was indeed probably between March and September. More than this, we cannot say.


In the next post we look at what Matthew says about the Star, and see if there are any clues that we can glean from Matthew and other contemporary texts.


[1] Here, Pope Gregory missed a trick because we still introduce a few extra days so, for the highest precision, millennial years should only be Leap Years if divisible by 4000. Technically, 2000 and 3000 should not be Leap Years, but 4000, yes.

[2] Russian moved to the Gregorian calendar in 1918 and Greece, in 1923, but the Orthodox church continues to use the Julian calendar for calculating the date of Christmas. Christmas Day will continue to be January 7th in these countries until the year 2101, when it will slip to January 8th.

[3] Most of the troops stationed on the Wall were from nearby countries such as Belgium who would been accustomed to a cooler, more humid climate anyway.

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