It’s generally accepted that early Christians adopted December 25^th as the day of Christ’s birth to co-opt the pagan celebration of the winter solstice. Some believe this fact undermines Christianity.

But according to Professor William Tighe, this “fact” may actually be a myth.

Based on his extensive research, Tighe argues that the December 25^th date “arose entirely from the efforts of early Latin Christians to determine the historical date of Christ’s death.” He also goes so far as to claim that the December 25^th pagan feast of the “’Birth of the Unconquered Sun’… was almost certainly an attempt to create a pagan alternative to a date that was already of some significance of Roman Christians.”

In the Jewish tradition at the time of Christ, Tighe explains, there was a belief in what they called the “integral age”—that the prophets had died on the same days of their conception or birth. Early Christians spent much energy on determining the exact date of Christ’s death. Using historical sources, Christians in the first or second century settled on March 25^th as the date of his crucifixion. Soon after, March 25^th became the accepted date of Christ’s conception, as well.

Add nine months—the standard term of a pregnancy—to March 25^th, and Christians came up with December 25^th as the date of Christ’s birth.

It is unknown exactly when Christians began formally celebrating December 25^th as a feast. What is known, however, is that the date of December 25^th “had no religious significance in the Roman pagan festal calendar before Aurelian’s time (Roman emperor from 270-275), nor did the cult of the sun play a prominent role in Rome before him.” According to Tighe, Aurelian intended the new feast “to be a symbol of the hoped-for ‘rebirth,’ or perpetual rejuvenation, of the Roman Empire…. [and] if it co-opted the Christian celebration, so much the better.”

As Tighe points out, the now-popular idea that Christians co-opted the pagan feast originates with Paul Ernst Jablonski (1693-1757), who opposed various supposed “paganizations” of Christianity.

I have never heard of the notion of “integral age,” and it seems a dollop of fudge to claim that it was conceptually important for someone to die on the “same day as his conception or birth.” Well, which is it? Moreover, I have never heard of the observance of the Crucifixion being fixed on March 25, or on any other date for that matter – Jesus was executed at Passover, which is a movable feast against the solar calendar. In observance of this, the celebration of Christ’s death and resurrection has always been movable as well. Wikipedia on the Computus: 

Easter is the most important Christian feast, and the proper date of its celebration has been the subject of controversyas early as the meeting of Anicetus and Polycarp around 154. According to Eusebius’ Church History, quoting Polycrates of Ephesus, churches in the Roman Province of Asia “always observed the day when the people put away the leaven“, namely Passover, the 14th of the lunar month of Nisan. The rest of the Christian world at that time, according to Eusebius, held to “the view which still prevails,” of fixing Easter on Sunday. Eusebius does not say how the Sunday was decided. Other documents from the 3rd and 4th centuries reveal that the customary practice was for Christians to consult their Jewish neighbors to determine when the week of Passover would fall, and to set Easter on the Sunday that fell within that week.

At some point it became important for Christians to ensure that the celebration of Easter did not coincide with Passover – and anyone who calculated it differently, like the Irish, was committing a grievous error. But note that in either case Easter was still movable. March 25 is the feast of the Annunciation, certainly, but only in relation to December 25, the (non-movable) feast of Christ’s birth.