It’s the most wonderful time of the year!
Stockings are filled with goodies, cups overflow with eggnog, and people embrace the spirit of peace and goodwill, assuming they have all the shopping done and don’t have to fight throngs of angry consumers trying to get that last minute item.
Oh, and we celebrate that Jesus was born. Now, back to the festivities!
Christmas is not only lucrative for retailers, but also for the handful of scholars who make the rounds on History channel specials on the Origins of Christmas, the Real Christmas, or anything else that can draw a few more eyes. Stacked between the Charlie Brown specials and re-runs of It’s a Wonderful Life, your whole family can gape in awe as some professor emeritus from some university bedazzles the world with speculations about a congruence of Jupiter and Saturn actually being the Christmas star.
Nor are dead tree media outlets immune from the Christmas glut. In normal circumstances a scholar saying something that most other scholars for the last couple hundred years have said would raise nary an eyebrow, but if that scholar happens to be the pope then all of a sudden the very foundations of what remains of Christendom are crumbling all around. Thus the Telegraph:
Shocking news- Jesus wasn’t born in AD 1! What, even 0 is out?
How will Christianity ever survive?
(The byline, of course, is laughable beyond belief, but the Telegraph has always proved itself to be gunning for humor in its religion reporting.)
The dating of Jesus’ birth has always involved a bit of speculation. After all, the closest historical records do not give a date nor even uncontroversially specify a year. That our knowledge of the events of this period are spotty at best and open to new evidence does not help matters.
But much the like other dates within the Christian calendar, the December 25 date for the celebration of Christmas has inevitably given rise to the rather popular notion that it originated as a pagan festival. According to the most widely accepted version of Christian Mythstory, Christmas was the church’s attempt to co-opt the pagan festival of Sol Invictus, which oh-so-conveniently fell on the 25th of December as well. Instituted by Emperor Aurelian in AD 274, the festival of the Unconquered Sun was the basis for Christians’ celebration of Jesus’ birth. Other versions go further, alleging a more insidious syncretism between Sol Invictus and Christmas.
After all, aren’t Christmas trees the purview of Germanic pagans? Nevermind that Sol Invictus was a Roman holiday… pagan trees!
The reactions by non-Christians and Christians to such a mythstory are so varied as to defy any generalization. Many Christians actually accept such a mythstory (like many others) at face value, without really knowing why.
Thus, the question is two-fold: how did the celebration of Christmas come about, and was it put in place to rival (or be part of) a pagan festival?
As with any question that involves festival dates in antiquity, there are no easy answers.
The ancient world did not have a unified calendar, and thus one nation/people group/whatever might use a solar calendar, another might use the lunar calendar, another might use a modification of either or both. Even amongst themselves ancients often had trouble keeping track of dates; dating an event from the ascension of one ruler or the founding of a city is only useful if meticulous records are kept or if there is enough stability and hegemony in the sphere of influence to ensure some sort of cultural memory. Trying to reconcile dates across cultural boundaries was no easy task.
And as the anecdote from the Telegraph demonstrates, trying to do so long after the fact can be even more challenging.
That is not to say, however, that the ancients did not care about dates. Much of Christian astronomy was actually born out of trying to create a calendar that could come up with the right date for Easter. (The Sun in the Church is a fascinating book which chronicles this long drawn out ordeal.) Even before Christianity became a major influence in the Roman Empire the east and west were hashing out the right date for Easter. The church historian Eusebius gives us this intriguing insight:
“A question of no small importance arose at that time [i.e. the time of Pope Victor, about A.D. 190]. The dioceses of all Asia, as from an older tradition, held that the fourteenth day of the moon, on which day the Jews were commanded to sacrifice the lamb, should always be observed as the feast of the life-giving pasch [epi tes tou soteriou Pascha heortes], contending that the fast ought to end on that day, whatever day of the week it might happen to be. However it was not the custom of the churches in the rest of the world to end it at this point, as they observed the practice, which from Apostolic tradition has prevailed to the present time, of terminating the fast on no other day than on that of the Resurrection of our Saviour. Synods and assemblies of bishops were held on this account, and all with one consent through mutual correspondence drew up an ecclesiastical decree that the mystery of the Resurrection of the Lord should be celebrated on no other day but the Sunday and that we should observe the close of the paschal fast on that day only.”[1. Eusebius, Church History V.23]
This date will be important later on.
The ancient world was not monolithic in either its religion, its festivals or the dates on which those festivals took place. A date of some significance in one place might mean nothing in another; something that used to be celebrated on one date might be moved, stopped for awhile, rehabilitated, or anything in between. As such, some amount of coincidence might be expected.
On the other hand, our knowledge of ancient religious practices is quite patchy, and much of it comes from sources long removed from original material. Thus, while the traditional date of some feast may be on a certain date, there are any number of reasons that it might originally have been sometime else, influenced by some event or celebration, etc. In some cases it is just as likely that the date of the pagan festival was influenced by a previous Christian celebration.
The various cults and festivals in honor of the sun (Sol) were quite varied- both in intensity and scope- so as to defy generalization. The ancient Roman world was in many respects a hodgepodge of belief and practice, sometimes small and insignificant and sometimes widespread; often exclusive and often over-lapping with other beliefs.
The sun, of course, figured prominently in many religions and cults, and while the Romans broadly viewed the sun in some supernatural way, that did not necessarily translate to divinity. The sun could be a metaphor, a deity, a symbol, have astrological significance, etc.
Some have tried to argue that Aurelian lifted (or attempted to lift) Sol to prominence in the pantheon, but the evidence is quite lacking. Aurelian did construct a temple to Sol, but there is no evidence that December 25 was chosen as the festival date. Earlier festivals to Sol were already in place, the traditional dates being August 8/9 or August 28. Often the connection to the winter solstice is stressed in this mythstory, but the Romans curiously seemed to not have cared much about that connection.
The inscription of the dedication of the temple of Sol does not in fact mention a date, and the earliest evidence for its connection to December 25 comes around 80 years later:
“there is no evidence that Aurelian instituted a celebration of Sol on that day [December 25]. A feast day for Sol on December 25th is not mentioned until eighty years later, in the Calendar of 354 and, subsequently, in 362 by Julian in his Oration to King Helios”[2. Steven Ernst Hijmans, Sol : the sun in the art and religions of Rome, p.588]
However, in Julian’s hymn even the date of December 25 as the date for Aurelian’s dedication is suspect. Aurelian had established quadrennial games in honor of the Sun (as mentioned in Calendar 354), and Julian seems to allude to them:
If after this I should say that we also worship Mithras, and celebrate games in honour of Helios every four years, I shall be speaking of customs that are somewhat recent. But perhaps it is better to cite a proof from the remote past.[3. Julian, Hymn to King Helios, 155, http://en.wikisource.org/wiki/Hymn_to_King_Helios]
It should be noted that Julian is intentionally saying that the quadrennial games are of recent invention, and then wishes to describe something pertaining to the honoring of the sun from even further back. He speaks of the various reasons that the New Year is celebrated at different times and then states:
But our forefathers, from the time of the most divine king Numa, paid still greater reverence to the god Helios.[4. ibid.]
For the rest of the section he describes how the ancient Romans supposedly revered Sol above all and, because of their close relation to him and their deep devotion, understood the correct time to celebrate the New Year. According to Julian this ancient knowledge was lost for a thousand years, only to be picked up anew:
But the truth of these facts was recognised, as I said, by a later generation. Before the beginning of the year, at the end of the month which is called after Kronos, we celebrate in honour of Helios the most splendid games, and we dedicate the festival to the Invincible Sun… But, in the cycle, immediately after the end of the Kronia follow the Heliaia.[5. ibid.]
By distinguishing between the quadrennial games of Aurelian as of recent invention and the supposedly traditional date for the celebration of Sol Invictus, the date of Sol Invictus which Julian recognized (December 25-ish) is distinct from the times set for what Aurelian established:
We certainly have no evidence that there were multiple quadrennial games for Sol. Julian clearly considers the agon he ascribes to Numa to be unrelated to these quadrennial agones, and yet Aurelian’s games would have been celebrated in 362 for the 23rd time. This must mean that they had been celebrated at a different time, and thus we can rule out December 25th as the date of Aurelian’s agones for Sol.[6. Steven Ernst Hijmans, Sol : the sun in the art and religions of Rome, p.589-590]
The evidence from Calendar 354 is equally questionable, since it actually mentions separate festivals for Sol:
August 28: Sol and Luna; 24 chariot races;
October 19-22: Ludi Solis, 36 chariot races;
December 25: Natalis Invicti, 30 chariot races.[7. ibid., p.591]
There are two difficulties present:
The first is that the sheer number of races in the October festival speak to greater importance, as well as betoken the quadrennial nature of these races. 24 chariot races was the norm, and during 354 there were 63 festivals with races, only four not having 24. Thus,
anyone surveying the calendar of festivities in honour of Sol would identify the period from October 19th to October 22nd as far more important than December 25th, and the festival of August 28th as far older.[8. ibid.]
The second difficulty is that the term Natalis Invicti is not necessarily related to the sun, but could generically refer to something or someone important:
In the calendar the term natalis (anniversary or celebration), which can be used for emperors, gods and heroes, and even events, is invariably followed by the primary name or term used to identify the emperor, god, or event whose natalis is celebrated. The single exception to this rule is here. Add to this that the date celebrated, the winter solstice of the Julian calendar, while astronomically important, had no significance that we know of in the Roman religious practices associated with the sun god, and it clear that the entry for December 25th is in every way problematic.[9. ibid. p.592]
Given the utterly exceptional nature of this entry, some scholars believe it to be a later interpolation added to buttress Julian’s introduction of Sol Invictus on December 25. His attempts to link a date- for which there is no other evidence- to the far reaches of antiquity causes one to suspect that he doth protest too much. After all, none of the other festivals of Sol had an astronomical significance; that it suddenly falls on the winter solstice seems far too convenient. Hijmans tantalizingly concludes:
None of this tells us when the natalis invicti of December 25th entered the Roman calendar, but on this evidence we must acknowledge that it is a real possibility that it did not do so until after the bishop of Rome first celebrated Christmas on that day – a pagan reaction to a Christian feast, perhaps, rather than vice versa.[10. ibid. p.592]
Having mostly answered the second question, the first question question remains: How did the date of Christmas come about?
The date of birth of Christ was not widely speculated on until the third century, although there are isolated texts from some writers which consider the question. Hippolytus, writing in the early third century, says that
For the first advent of our Lord in the flesh, when he was born in Bethlehem, was December 25th, a Wednesday, while Augustus was in his forty-second year, but from Adam, five thousand and five hundred years. He suffered in the thirty-third year, March 25th, Friday, the eighteenth year of Tiberius Caesar, while Rufus and Roubellion were Consuls.[11. Hippolytus, Commentary on Daniel, 4.23.3]
There is debate as to whether the date of the 25th of December is a later interpolation, but regardless of that another consideration surfaces in Hippolytus’ Chronicon in which he states that
…from Adam until the transmigration into Babylon under Jeconiah, 57 generations, 4,842 years, 9 months. And after the transmigration into Babylon until the generation of Christ, there was 14 generations, 660 years, and from the generation of Christ until the Passion there was 30 years…[12. Hippolytus, Chronicon, 686-688]
Hippolytus believes that Jesus’ passion occurred on the same day as the creation of the world, and given the 9 months he interposes for Christ’s generation, also believes that Jesus was conceived on the same calendar day as he died. (That is, March 25.) As such, the 9 months figure is meant to coincide with the gestation period, leading right to the birth date of December 25. Thus, even if the date itself is a later interpolation, Hippolytus’ own calculations intend Dec. 25 as the date for Jesus’ birth.
Clement of Alexandria
Another writer named Clement of Alexandria also hints at the date of Dec 25. In his Stromata he actually lays out a few dates:
From the birth of Christ, therefore, to the death of Commodus are, in all, 194 years, 1 month, 13 days. And there are those who have determined not only the year of our Savior’s genesis, but even the day, which they say took place in the twenty-eighth year of Augustus on the 25th of Pachon… And treating of his passion, with very great accuracy, some say that it took place in the sixteenth year of Tiberius, on the 25th of Phamenoth, but others the 25th of Pharmuthi and others say that on the 19th of Pharmuthi the Savior suffered. Indeed, others say that he came to be on the 24th or 25th of Pharmuthi.”[13. Celement of Alexandria, Stromata, 1.21.145-146]
One indication here is that there is no definite date in play within the wider Christian calendar but several competing calculations. However, like Hippolytus he seems to link the date of Jesus’ conception with the date of his death. If Jesus’ death was indeed on the 25th of a month, his birth date following 9 months later would naturally fall on the 25th.
To be fair, Clement’s calendar is hard to reconcile with others, as the actual equinoxes and the civil observance of those equinoxes did not always coincide. Even though the dates he gives are on the Egyptian calendar, the dates seem to originate from elsewhere.
Differences in calendars can reasonably explain why there is such a great variance of dates; for example, the tenth month for the Romans was December, whereas for Athenians it was April; for Alexandrians it would have fallen in June. Additionally, the month of Pharmuthi is five days different from the Roman month of April, thus giving the difference of the 19th and the 24th. Lastly, it is well-known that different cultures mark the beginning of a day at different times; thus, for Romans a day may begin differently than for Egyptians, giving us the difference of the 24th/25th.
Although not directly tackling the issue, Tertullian gets at the Dec 25 date in a round-about way by informing us that the date of the crucifixion (Nisan 14) is equivalent to March 25 in the Roman calendar:
And the suffering of thisexterminationwas perfected within the times of the lxx hebdomads, under Tiberius Cæsar, in the consulate of Rubellius Geminus and Fufius Geminus, in the month of March, at the times of the passover, on the eighth day before the calends of April, on the first day of unleavened bread, on which they slew the lamb at even, just as had been enjoined by Moses.[14. Tertullian, An Answer to the Jews]
More writers and more dates could be quoted, but by the middle of the 4th century the date of December 25 for the celebration of Christ’s birth seems to have been fairly well established. In contradiction to the assumption that Christians were attempting to supplant Sol Invictus or Natalis Invictus, most Christian writers of the time saw the date of the birth of Christ as flowing naturally out of the link established between the dates of his death and conception. A pseudonymous work attributed to Chrysostom declares:
Therefore our Lord was conceived on the eighth day of the kalends of April in the month of March, which is the day of the passion of the Lord, and of his conception. For on the day he was conceived, on the same day he suffered.[15. De Solstitia et Aequinoctia Conceptionis et Nativitatis Nostri Iesu Christi et Iohannis Baptistae]
Chrysostom himself seems to have calculated the date based on the rotation of temple priests:
So it was then that the promise was made to Zecharias. The time of the promise was that of the feast of tabernacles and of the fasting, for this is that which was written, “Humble your souls” (Lev. 16:29). The feast was kept among the Jews about the last of the month of Gorpiaios, as ye witness (There were many Jews in Antioch)—The six months of the conception of Elizabeth are Hyperberetaios- October, Dios- November, Apellaios- December, Audynaios- January, Peritios- February, and Dystros- March. After this sixth month came the commencement of the conception of Mary. Whence reckoning nine months we reach the present day (December 25th).[16. St. John Chrysostom, Diem Natalem Dominus Nomine Jesu Christi]
St. Augustine also links the December 25 date with Jesus’ conception and death:
For he [Jesus] is believed to have been conceived on the 25th of March, upon which day also he suffered; so the womb of the Virgin, in which he was conceived, where no one of mortals was begotten, corresponds to the new grave in which he was buried, wherein was never man laid, neither before him nor since. But he was born, according to tradition, upon December the 25th.[17. St. Augustine, On the Trinity]
Tin Foil Hat Time! (With Tinsel)
Given the lack of evidence for the pre-Christian influence of Sol Invictus (or Natalis Invictus) and the preponderance of evidence for Christians thinking that Jesus was really born on Dec 25 because of the date of the crucifixion, from whence does this pernicious mythstory derive?
In some ways it begins with Christian writers. Even the Catholic Encyclopedia, which is usually a fairly good source for ecclesiastical history, manages to botch a quotation from pseudo-Cyprian, which is usually presented as:
O the splendid and divine Providence of the Lord, that on that day, even at the very day, on which the Sun was made, Christ should be born.[18. Pseudo-Cyprian, De Pascha Computus]
But this quotation is incomplete, for the entirety places it in context:
O! The splendid and divine Providence of the Lord, that on that day, even at the very day, on which the Sun was made, 28 March, a Wednesday, Christ should be born [nascor]. For this reason Malachi the prophet, speaking about him to the people, fittingly said: “Unto you shall the sun of righteousness arise, and healing is in his wings.” [Malachi 4:2]
As is clear, pseudo-Cyprian places the creation of the sun (not necessarily a birth) four later than March 25 on March 28. December 25 doesn’t even enter into the picture, and if this is compared (and contrasted) with other sources which place Jesus’ death on the anniversary of the creation of the world, there is little reason to suspect the author has any intention other than linking Jesus’ birth/death with the creation already described in the scriptures and calculated according to Jewish calendrical tables.
St. Chrysostom provides one of the most smoking of the supposed smoking guns in this unpublished homily:
Moreover the Lord is born in the month of December in the winter on the 8th Kalend of January when the ripe olives are gathered, so that the oil, that is the chrism, may be produced, moreover they call it the birthday of the unconquered One. Who in any case is as unconquered as our Lord, who conquered death itself? Or why should they call it the birthday of the sun; he himself is the sun of righteousness, concerning whom malachi, the prophet, spoke: “The Lord is the author of light and darkness, he is the judge spoken of by the prophet as the Sun of Righteousness.[19. De solstitiis et aequinoctiis]
A footnote from the same quotation (apparently listed in another work- Sermo de Nativitate S. Joannis Baptistae) states the following:
The preceding lines of this quotation from Chrysostom (Hom. 31) plainly state that Christ’s birthday has been fixed upon the day of the birth of Mithras: “On this day (the birthday of Mithras) also the birthday of Christ was lately fixed at Rome in order that whilst the heathen were busied with their profane ceremonies, the Christians might perform their holy rites undisturbed.”[20. Christmas and the Nativity of Mithras, Rev. Robert Sinker, p.4]
A few difficulties are immediately presented. First, the quotation from De solstitiis et aequinoctiis is actually pseudonymous, although until recently many historians erroneously attributed them to St. Chrysostom. Secondly, there is no reason to suspect that the parenthetical references to Mithras are necessitated by the text, but, given the rather poor linkage already seen between Christmas and pagan festivals and the rather generic character of Natalis Invictus, there is just as much reason to suspect that the translator is assuming too much.
Unfortunately, I have not been able to find any source material for the quotations in question. Notwithstanding that, is this really a smoking gun?
The date of Christmas in the West and the East varied, the West generally accepting the date of the 25th of Dec and the East the 6th of January. St. Chrysostom notably pushed for the celebration of Christmas on the 25th from the 6th, a move not suffered lightly. The spurious nature of the motivation presented here (at least for Chrysostom) lies in the fact that in his moving of the date, Chrysostom argued that the date was corroborated by Roman census records, that if the date hadn’t been correct the celebration of Christmas wouldn’t have spread so quickly, and that the information in Luke’s gospel allows one to work out the day, as seen above.
However, even the explicit linking of the fixing of the date on Natalis Invictus does not establish the mythstory. If we keep in mind that some eastern churches changed their celebration from Jan 6 to December 25, such a move would quite naturally be perceived as being ‘fixed.’ More to the point, the author here indicates that the celebration of Christmas at the very least is not an outgrowth of Natalis Invictus or a synchrenization with it, but rather a declaration of war against it. The author clearly intends what he is writing to be understood ironically, for while the pagans engage in their revelry the Christians demonstrate their piety.
Pope Leo I
Other writers (such as Pope Leo I) are often adduced in connection with the Natalis Invictus link:
When the sun rises at daybreak, there are some people so foolish as to worship it from the highest elevations; even some Christians think they are acting piously by following this practice, so that before entering the basilica of St. Peter the apostle, dedicated to the only living and true God, when they have gone up the steps leading to the porch at the main entrance, they turn around to face the rising sun and, inclining their heads, bow in honor of the brilliant disk. This behavior, partly due to the vice of ignorance and partly to the spirit of paganism, upsets and saddens us very much. Even if some of them do worship the creator of that beautiful light rather than the light itself, which is a creature, they should still abstain from giving the appearance of that worship, because if someone who has turned away from the cult of the gods notices the same custom among us, would that person not return to the old beliefs thinking that probably Christians and nonbelievers are doing the same thing?[21. Leo I, Sermon VII]
The force of such a connection in relation to this quote is only as powerful as the demonstrable outgrowth of Christmas from Sol Invictus. Thus, Leo I’s reprimandings of Christians for worshipping the sun could just as easily be explained with a date of Natalis Invictus postdating the celebration of Christmas on Dec 25.
12th Century Marginal Note
But the smokiest of smoking guns comes sometime in the 12th century, found in a marginal note of a gloss:
“The Lord was born in the month of January, on the day on which we celebrate the Epiphany; for the ancients observed the Nativity and the Epiphany on the same day, because he was born and baptized on the same day. Also still today the Armenians celebrate the two feasts on the same day. To these must be added the Doctors who speak at the same time of one and the other feast. The reason for which the Fathers transferred the said solemnity from the sixth of January to the twenty-fifth of December is, it is said, the following: it was the custom of the pagans to celebrate on this same day of the twenty-fifth of December the feast of the birth of the sun. adorn the solemnity, they had the custom of lighting fires and invited even the Christian people to take part in these rites. When therefore, the Doctors noted that the Christians were won over this custom, they decided to celebrate the feast of the true birth this same day; the sixth of January they made to celebrate the Epiphany. They have kept this custom until today with the rite of lighted fire.”[22. Thomas J. Talley, The Day of His Coming, p.12]
The chief strength of this evidence is that most quotations of it begin with “the reason for this…” and continue on, presenting the reason for the shift in isolation. However, from the opening where the author states what he believes to be the actual birthday (Jan. 6), it is just as reasonable to assume that (as a member of the eastern church) he rejects the Dec. 25 date for the solemnity, and that the reasons he discusses for its shift are intended polemically:
Clearly, the scholiast is orthodox and he rejects the date of December 25th. One such late, and obviously hostile, source has little value in this case. I would argue that the evidence is clear.[23. Steven Ernst Hijmans, Sol : the sun in the art and religions of Rome, p.594]
Even if we grant that he is speaking without polemical intent, there is no reason to assume that the reasons he propounds are actually representative of why the date of Dec. 25 was chosen. The preponderance of earlier evidence indicates that most of those who argued Dec. 25 was the date actually believed it was.
Making a Myth
In reality, these two smoking guns are actually shooting blanks, yet scholars in the late 18th century (caught up in the furor of the relatively new field of comparative religion) through the late 19th century latched on to the idea that Natalis Invictus was the source of Christmas, the latter being a Christianization of the former.
One major (and until recently unchallenged) assumption was that the sheer coincidence of the winter solstice virtually guaranteed some pagan connection, given the relatively universal pagan penchant for celebrations around solstices. However, the evidence of the Roman sun-cult celebrations is that they seemed to have little to nothing to do with the actual astronomical phenomenon, for whatever reason. It is not until Julian that we find an unambiguous relation of Sol Invictus (or Natalis Invictus) with Dec. 25, a date on which the celebration of Christmas could have been celebrated for decades. The difficulty with the generic solstice assumption is that it tended to bias all mentions of sun imagery in either pagan or Christian literature of the time towards some sort of over-arching solar hegemony:
In the Roman Empire, the divine nature of Sol was open to broad interpretation. As a heavenly body, the sun was often used – together with Luna – as a cosmic symbol or metaphor for eternity. The astronomical reality of the sun and the moon precluded such symbolism from being exclusively pagan, and the evidence of the De solstitia et aequinoctia conceptionis et nativitatis domini nostri iesu christi et iohannis baptistae, as well as the passages of a wide range of homilies collected by Heim (1999) suggest that it was readily adopted by Christians.[24. ibid., p.594-595]
From the Christian literature, at least, the integral link between God and the sun is established in the creation narrative, and the sun is often used metaphorically for the divine. From the Christians writings in this period we can find them linking Christ as the sun to the prophesies in Malachi, and in the calculations for his nativity it are these scriptural (and Jewish calendrical) considerations that drive the speculation. Even the De solstitiis et aequinoctiis makes quite clear that we should see the date of December 25th not in isolation, but as part of a cosmic- symbolic system:
The author points out that the birthday of John the Baptist was exactly 6 months before that of Jesus, meaning that he was born on the summer solstice. This means that John was conceived in the autumn – on the equinox to be exact – while Jesus was conceived on the vernal equinox. Having built up and argued this cosmic symbolic system throughout his homily, the author at the very end, in the aside quoted by Usener (supra), deals with the problem that the winter solstice also happens to be the “birthday of [Sol] Invictus”. That Christ was born on that day can be no problem, he argues, as Christ is the true “sun of justice”.[25. ibid. p.594]
Thus, while the Christians during the time when Sol Invictus was unambiguously celebrated knew that their pagan neighbors “called this day the “birthday” of Sol Invictus, this did not concern them and it did not play any role in their choice of date for Christmas.”[26. ibid., p.595]
In the end, the best evidence we have for why early Christians chose Dec. 25 as the date of the celebration of the Nativity is because they actually thought it happened then. It may be that the coordination of solstices was convenient (they would have argued it was providential), but there is little reason to believe the date of Christmas was ever meant to be anything other than a celebration of the Nativity, since they believed it to have occurred on December 25th. It would be too laborious to go into the merits of such a date, but the mythstory is not based on the date being accurate, but rather the origin of it.
Granted, the Christians in the 4th century did not live in a bubble, and no doubt were aware of some of the correspondences being drawn between the Unconquered Sun and the Unconquered Son; indeed, at least one author seems to have recognized and delighted in such a connection being made. Given the likelihood of Sol Invictus being established by Julian in response to Christmas, it is with perhaps a bit of a snicker that ancient authors would have perceived the mythstory popularly swallowed for the last two hundred years.