Christmas

The earliest evidence for the date is a Roman document of 354, and it is worth reading precisely because it is regularly misdescribed.

The Chronography of 354 is a compiled almanac. One of its parts, a civil calendar, records for the eighth day before the kalends of January the entry N INVICTI CM XXX, birthday of the Unconquered, thirty races ordered, which is the oldest literary reference to a festival of Sol Invictus on that date. A different part, the Depositio Martyrum, a list of commemorations, records for the same day: born Christ in Bethlehem of Judaea. That is the earliest reference to the nativity kept as an annual feast.

So a single document attests both observances in Rome by the mid fourth century. What it does not do is establish which came first or that one produced the other, and this is where popular accounts overreach.

The rival explanation, argued at length by Thomas Talley and others, is the calculation hypothesis: an early Christian tradition held that a prophet died on the same date he was conceived, put the crucifixion at 25 March, therefore put the conception at 25 March, and arrived at 25 December by counting nine months. That reckoning is attested in the third century, in Hippolytus and in an African treatise on the computation of Easter, before any evidence of a December feast. On this account the date is derived internally and its coincidence with the solar festival is a consequence of both being anchored near the solstice.

Neither hypothesis has won. Both are held by serious historians of liturgy.

The claim that Christmas is Saturnalia renamed is repeated everywhere and does not survive contact with the Roman calendar.

Saturnalia was 17 December, extended in the imperial period to the 17th through the 23rd. It is not 25 December. Its characteristic elements, the reversal of master and slave, the licence, the gambling, the mock king, have no counterpart in the Christian feast, and the gift-giving associated with it belonged to the Sigillaria at the end of the run. Ancient Christian writers who wanted to attack pagan festivals were entirely willing to name them, and none of them says the nativity feast replaced Saturnalia.

The Sol Invictus argument is stronger because the date matches, but it too has a difficulty: the festival of the Unconquered Sun on 25 December is first attested in the very document that first attests the Christian feast, so the claim that Christianity took over an established solar holiday rests on evidence no earlier than the thing it is meant to explain. Aurelian's promotion of the cult in 274 is real; that he fixed a 25 December festival is an inference.

Some later Christian writers, from the fourth century onward, do draw the solar comparison, calling Christ the true sun. That is theological appropriation of imagery, and it is evidence that the coincidence was noticed. It is not evidence about origins.

The evergreens, the tree, the log and the wreath are a separate matter again, largely medieval and early modern and mostly northern European.

This is the most misunderstood date in the Christian calendar, and the explanation contains no theological disagreement at all.

Every church that keeps the nativity keeps it on 25 December. The difference is which calendar the 25th is counted on. The Julian calendar, in use in the Roman world from 46 BCE, assumes a year of 365.25 days, which is about eleven minutes too long. Over centuries the error accumulated, and by 1582 the calendar had drifted ten days out of step with the seasons. Gregory XIII corrected it by dropping ten days and by changing the leap year rule so that centurial years are leap years only when divisible by 400.

Catholic states adopted the reform at once, Protestant states over the following two centuries, and Britain in 1752. Orthodox churches did not, and the offset has since grown to thirteen days. So 25 December in the Julian reckoning falls on 7 January in the Gregorian one, and will do until 2100, when the gap becomes fourteen days and the correspondence shifts to 8 January.

Not all Orthodox churches are on the old calendar. In 1923 a congress at Constantinople adopted a revised Julian calendar for fixed feasts, and the churches of Constantinople, Greece, Romania, Bulgaria and others follow it, so they keep the nativity with the West. Russia, Serbia, Georgia, Jerusalem and the monasteries of Athos retain the old calendar. The Armenian church is a separate case again, keeping the nativity on 6 January with the Epiphany, which reflects the older undivided feast.

Nobody is celebrating a different event, and nobody is thirteen days late.