ORIGIN OF DATE The Gospels
Concerning the date of Christ's birth the Gospels give no help; upon their data contradictory arguments are based. The census would have been impossible in winter: a whole population could not then be put in motion. Again, in winter it must have been; then only field labour was suspended. But Rome was not thus considerate. Authorities moreover differ as to whether shepherds could or would keep flocks exposed during the nights of the rainy season. Zachary's temple service
Arguments based on Zachary's temple ministry are unreliable, though the calculations of antiquity (see above) have been revived in yet more complicated form, e.g. by Friedlieb (Leben J. Christi des Erlösers, Münster, 1887, p. 312). The twenty-four classes of Jewish priests, it is urged, served each a week in the Temple; Zachary was in the eighth class, Abia. The Temple was destroyed 9 Ab, A.D. 70; late rabbinical tradition says that class 1, Jojarib, was then serving. From these untrustworthy data, assuming that Christ was born A.U.C. 749, and that never in seventy turbulent years the weekly succession failed, it is calculated that the eighth class was serving 2-9 October, A.U.C. 748, whence Christ's conception falls in March, and birth presumably in December. Kellner (op. cit., pp. 106, 107) shows how hopeless is the calculation of Zachary's week from any point before or after it. Analogy to Old Testament festivals
It seems impossible, on analogy of the relation of Passover and Pentecost to Easter and Whitsuntide, to connect the Nativity with the feast of Tabernacles, as did, e.g., Lightfoot (Horæ Hebr, et Talm., II, 32), arguing from Old Testament prophecy, e.g. Zacharias 14:16 sqq.; combining, too, the fact of Christ's death in Nisan with Daniel's prophecy of a three and one-half years' ministry (9:27), he puts the birth in Tisri, i.e. September. As undesirable is it to connect 25 December with the Eastern (December) feast of Dedication (Jos. Ant. Jud., XII, vii, 6). Natalis Invicti
The well-known solar feast, however, of Natalis Invicti, celebrated on 25 December, has a strong claim on the responsibility for our December date. For the history of the solar cult, its position in the Roman Empire, and syncretism with Mithraism, see Cumont's epoch-making "Textes et Monuments" etc., I, ii, 4, 6, p. 355. Mommsen (Corpus Inscriptionum Latinarum, 12, p. 338) has collected the evidence for the feast, which reached its climax of popularity under Aurelian in 274. Filippo del Torre in 1700 first saw its importance; it is marked, as has been said, without addition in Philocalus' Calendar. It would be impossible here even to outline the history of solarsymbolism and language as applied to God, the Messiah, and Christ in Jewish or Christian canonical, patristic, or devotional works. Hymns and Christmas offices abound in instances; the texts are well arranged by Cumont (op. cit., addit. Note C, p. 355).
The earliest rapprochement of the births of Christ and the sun is in Cyprian, "De pasch. Comp.", xix, "O quam pr
æclare providentia ut illo die quo natus est Sol . . . nasceretur Christus." — "O, how wonderfully actedProvidence that on that day on which that Sun was born . . . Christ should be born."
In the fourth century, Chrysostom, "del Solst. Et Æquin." (II, p. 118, ed. 1588), says: "Sed et dominus noster nascitur mense decembris . . . VIII Kal. Ian. . . . Sed et Invicti Natalem appelant. Quis utique tam invictus nisi dominus noster? . . . Vel quod dicant Solis esse natalem, ipse est Sol iustitiæ." — "But Our Lord, too, is born in the month of December . . . the eight before the calends of January [25 December] . . ., But they call it the 'Birthday of the Unconquered'. Who indeed is so unconquered as Our Lord . . .? Or, if they say that it is the birthday of the Sun, He is the Sun of Justice."
Already Tertullian (Apol., 16; cf. Ad. Nat., I, 13; Orig. c. Cels., VIII, 67, etc) had to assert that Sol was not the Christians' God; Augustine (Tract xxxiv, in Joan. In P.L., XXXV, 1652) denounces the heretical identification of Christ with Sol.
Pope Leo I (Serm. xxxvii in nat. dom., VII, 4; xxii, II, 6 in P. L., LIV, 218 and 198) bitterly reproves solar survivals — Christians, on the very doorstep of the Apostles' basilica, turn to adore the rising sun. Sun-worship has bequeathed features to modern popular worship in Armenia, where Christians had once temporarily and externally conformed to the cult of the material sun (Cumont, op. cit., p. 356).
But even should a deliberate and legitimate "baptism" of a pagan feast be seen here no more than the transference of the date need be supposed. The "mountain-birth" of Mithra and Christ's in the "grotto" have nothing in common: Mithra's adoring shepherds (Cumont, op. cit., I, ii, 4, p. 304 sqq.) are rather borrowed from Christian sources than vice versa. Other theories of pagan origin
The origin of Christmas should not be sought in the Saturnalia (1-23 December) nor even in the midnight holy birth at Eleusis (see J.E. Harrison, Prolegom., p. 549) with its probable connection through Phrygia with the Naasene heretics, or even with the Alexandrian ceremony quoted above; nor yet in rites analogous to the midwinter cult at Delphi of the cradled Dionysus, with his revocation from the sea to a new birth (Harrison, op. cit., 402 sqq.). The astronomical theory
Duchesne (Les origines du culte chrétien, Paris, 1902, 262 sqq.) advances the "astronomical" theory that, given 25 March as Christ's death-day [historically impossible, but a tradition old as Tertullian (Adv. Jud., 8)], the popular instinct, demanding an exact number of years in a Divine life, would place His conception on the same date, His birth 25 December. This theory is best supported by the fact that certain Montanists (Sozomen, Hist. Eccl., VII, 18) kept Easter on 6 April; both 25 December and 6 January are thus simultaneously explained. The reckoning, moreover, is wholly in keeping with the arguments based on number and astronomy and "convenience", then so popular. Unfortunately, there is no contemporary evidence for the celebration in the fourth century of Christ's conception on 25 March. Conclusion
The present writer in inclined to think that, be the origin of the feast in East or West, and though the abundance of analogous midwinter festivals may indefinitely have helped the choice of the December date, the same instinct which set Natalis Invicti at the winter solstice will have sufficed, apart from deliberate adaptation or curious calculation, to set the Christian feast there too.