As far as the day of Jesus’s birth is concerned, Dionysius adapted the date of the festival of Sol Invictus. He did this to christianise a very popular pagan ritual, thus making the Christian celebration easier for the masses to accept. Such practice was common in the early church as Christianity struggled to supplant the ancient practices of the time. Sol Invictus had been celebrated for many centuries, by the Celts and the Romans, in a way that would be strikingly familiar to us today: decorating the houses with green branches; meals and parties; the giving and receiving of presents; etc. (who says that Christmas is an invention of our modern, commercialised times?).

Dionysius, thus, put the Nativity on December 25^th 1AD. Curiously, almost at the end of the first year after Christ. He used the reigns of the emperors of Rome to calculate the date of the birth of Christ, but made two important errors in his calculations. One was to forget to include a Year 0, so that his calendar jumps straight from 1BC to 1AD. The other was to forget the four years that Caesar Augustus reigned under the name of Octavian. In other words, or modern calendar has a 5-year error built into it. One consequence is that Jesus was, as a result, illogically born several years before Christ.

Although there is some evidence that this date had been used for at least two centuries, Dionisius formalised it. Various alternative dates had been proposed for the Nativity by other authorities in the early church, but this was the one which became globally accepted.

There is another curiosity here which does not seem to have been picked up previously. In the 16^th Century most of Europe changed from the Julian to the Gregorian calendar, with a jump of 10 days in the date (to be different, England adopted this change some time afterwards, whilst some countries have never adopted it and still use the old Julian calendar). However, when Pope Gregory shifted the year by 10 days to correct the seasons, the date of Christmas remained the same. Thus our December 25^th is not same as Dionisius’s!

King Herod is a key player in the history of the Nativity. We know that he died shortly afterwards, but the date of his death was uncertain for some years. The clue that we have is that he died shortly after a lunar eclipse that was visible for Jericho and that he died during the lunar month between this eclipse and Passover.

Fortunately, lunar eclipses are not so common that there is a real danger of confusion. In the Jewish calendar, based on the lunar month, Passover falls in the month of Nissan, the seventh month of the year. The eclipse which fulfils the criteria was a 35% partial eclipse seen on the night of March 13th/14th 4BC. In other words, King Herod almost certainly died in late March, or early April of 4BC. Read about Passover and lunar eclipses at the time of the Nativity here.

One of the major problems in ascertaining the date of the birth of Jesus is the confusion surrounding the account in Luke’s Gospel about the census. Luke states that Quirinius was Governor of Syria at the time. Unfortunately, Quirinius did not become Governor of Syria until 6AD. This led some experts to place the Nativity as late as 7AD, completely in contradiction with Matthew’s Gospel which states that Jesus was born in times of Herod the Great. Which of the two was right? Or, could they both be right?

If we assume that Matthew was right and that Herod was still alive, the census would have had to have been before 4BC. However, Quirinius was Governor’s legate in Syria between 6 and 5BC. Perhaps Luke, writing around 80-85AD, confused the two posts.

Similarly, Caesar Augustus ordered censuses on three occasions: 28BC, 8BC and 14AD. The only one of these around the right time was the 8BC date, for which the order was recently located in Ankara (Turkey); the 14AD date creates yet another contradiction and the 28BC date is far too early. How can we resolve some of these contradictions? (More)

As we have seen, Dionysius picked this date for other reasons than really believing that Jesus was born on December 25^th. The only real clue that we have about the true date is from Luke’s Gospel which, as we have seen, is an unreliable guide. Luke claims that there were shepherds watching over their flocks at the time of Jesus’s birth. As has been pointed out in the past, in Palestine, the winter weather is sufficiently bad that the flocks would have been under shelter at this time. Although snow is not too common, rain and cold is sufficient to stop the animals from being left out to graze. In Spring (March-April), lambing time would oblige the shepherds to watch their flocks by night to help ewes in distress. This suggests that Jesus was born in March or April.

More tenuous are two indirect clues. The first is that the inn was full. This would have been the case particularly in Passover. The second is that Jesus is referred to as "the holy lamb of God"; this, as the British expert, Colin Humphreys points out, could mean that Jesus was born at the time that the Passover lambs were selected. Both these clues would suggest a March-April date too for the first Christmas.

Bearing in mind the points made above, we can only guess at the date when Jesus was born. It was almost certainly before 4BC and the death of Herod, probably 1-2 years beforehand. It was probably in Spring. This leaves a "best guess" of March 5BC, although 6BC is a definite possibility. An earlier date, for example, 7BC, seems much less likely. However, with so much contradictory evidence, we may never be sure that we have the right date. One happy result of this suggested date is that Dionysius would be vindicated as the year agrees with his when the 5 year error is taken into account.