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 solar symbolism 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 præclare providentia ut illo die quo natus est Sol . . . nasceretur Christus." — "O, how wonderfully acted Providence 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.
