This is actually a far more complicated topic than one would imagine — as all (ancient) history is, once one begins to delve deeper than typical narratives and textbook caricatures. Even so, the early Christian celebration of Christmas is a particularly difficult topic of research, since it requires mastery of the normal primary sources and comparative study of the ancient civil and religious calendars of the Babylonian, Jewish, Greek and Roman traditions (all of which influenced particular Christian Churches).
The only decent modern study I know of is Thomas J. Talley’s The Origins of the Liturgical Year, which manages to treat all of these things with equanimity and scholarly precision. Unfortunately, it is also quite dense, prone to tangents and given to rather esoteric and detailed use of ancient chronologies. Nevertheless, if you really want to figure all of this out -- and you have some background in ancient history, Latin, French and German -- Talley is your man.
If the prospect of such a read sounds arduously boring, here are a few bullet points I remember from reading and reflecting on the text more carefully a couple of years ago:
1) Ancient Greek and Roman religion had many, many feast days and celebrations. In fact, the cultic aspect of Roman religion was much like our own tradition, in that there were feasts and commemorations of this or that god or this or that event every day. Thus, if Christians’s were to choose ANY day to celebrate a particular event in Christ’s life, it would naturally fall on some pagan holiday. That the Christian choice of Dec. 25 for Christmas happens to fall on a pagan festival is therefore hardly surprising — nor is it scandalous.
2) Pagan festivals, specifically the festivals on and around Dec. 25 varied greatly. In some areas of the empire (and at some times), it was a significant feast; in other areas (and at other times), it was not.
3) In Italy, and in Latin-influenced areas generally, the Saturnalia lasted from Dec. 17 to Dec. 24, which was followed on Dec. 25 by the Brumalia, the feast of the shortest day. Traditionally, this was certainly a solar feast, since Dec. 25 was “the first day of the new sun, and the last day of the old” (as Ovid so famously put it in his Fasti: “Bruma novi prima est, veterisque novissima solis”). Many have taken this as proof that the Christians simply accommodated their feast of Christ’s birth to pagan practice. As Talley writes: “From the time of Paul Ernst Jablonski and the Bollandist Jean Hardouin, both in the eighteenth century, it has been common to account for the Christian celebration of the nativity of Christ on December 25 as a Christian adaptation of the Roman winter solstice festival, the Natalis solis invicti.” (Talley 88)
4) Such a narrative, however, misses a number of important facts. Talley continues: “That festival was established on December 25 by the emperor Aurelian in A.D. 274, and it seems likely that the same date was the occasion of Aurelian’s dedication of a temple to the sun god in the Campus Martius.” (Talley 88)
5) In other words, the Romans did not observe Dec. 25 as a feast of Sol Invictus until A.D. 274. Before that time, as Gaston Halsberghe shows in his major study The Cult of Sol Invictus, indigenous Roman sun cults were not very interested in Dec. 25, preferring to celebrate on August 28, which was the festival for the foundation of the temple of the sun at the Circus Maximus.
6) Dec. 25 and the winter solstice, therefore, was not extremely important to early Roman cultic manifestations of Sun worship, and its importance was lessened even more in the second century, when Romans abandoned more traditional cults and began to adopt the practices of eastern sun cults, e.g. Mithraism and the cult of Sol Invictus Elagabal -- both of which were very popular throughout the Empire. Neither cult assigned any importance to the winter solstice.
7) Thus, Halsberghe, Talley and many other scholars have shown that “the distinctive importance of that day [Dec. 25] must be assigned to the attempt of Aurelian to refound the cult of Sol Invictus as a genuinely Roman religion,” (Talley 89). Halsberghe (and, to lesser degree, Henry Chadwick) even go so far as to suggest that Aurelian spent so much effort on establishing the cult of Sol Invictus (with its strongly monotheistic and syncretistic theology, and its significant feast day on Dec. 25) in part because he wanted to introduce a Roman alternative to the increasingly powerful Christian movement (by this time, even pagan sources show that Roman emperors were aware of Christianity and its basic doctrines/practices).
8 ) Enter some anti-Donatist writings, which confirm that Christians had been celebrating Christmas on Dec. 25 in North Africa since at least 311, possibly even earlier than 300, depending on how you interpret the sources. Talley argues this based on a number of detailed readings I won’t bore you with. Talley writes: “A date before 312 would place Christmas prior to the Church’s enjoyment of the protection of Constantine, and that would set the most frequently encountered explanation of the origin of Christmas in a new and more problematic context. That most common explanation has been, and probably is today, the derivation of the feast of the nativity from a Roman pagan festival on the winter solstice, set on December 25 in the Julian calendar at its institution in 45 B.C.”
9) Thus, we have specific proof that Christians were celebrating Christmas in North Africa only 25 years after Aurelian had begun to reinstate Sol Invictus. Are we to assume that Christians would start celebrating such a feast as an accommodation to such a recent shift in pagan practice, or is it more likely that Christians either (a) had been doing so in some areas for longer, or (b) did so for other reasons?
[To Be Continued]