“NATIVITY, Feast of the. Similarly to other comparable feasts (6 or 10 Jan, 18 Nov, 28 March), in Rome the tradition developed of keeping the feast of Christmas on 25 Dec; this dates to ca. 336, though it is mentioned for the first time in the Chronography of 354. The Roman calendar indicates for 25 Dec, a day of the rebirth of the sun after the winter solstice, the birth of Mithras and public games in honor of the Sol Invictus, the cult of which the emperor Aurelian had introduced at Rome in 257. This apologetic context –Christ as the true Sol iustitiae (Mal 3:20)–was behind the introduction of the feast of Christmas in the Roman calendar. Further, chronological reasons relating to the other dates of the life of Christ (e.g., the Annunciation, 25 March) may have played a certain role. In 380 the feast was introduced in Constantinople, in 432 in Alexandria, and in 439 to Jerusalem, where it did not become established, however, until the Justinian era. There are numerous Christmas homilies in Latin and Greek, beginning with that of ps.- Optatus of Milevis (CPL 245). The oldest liturgical formulas may be found in the Sacramentarium Veronese. From the time of Gregory the great we find the characteristic triplicate Christmas Masses (Hom. ev. 8), the celebrated in S. Maria Maggiore, St. Anastasia and St. Peter’s” (Encyclopedia of Ancient Christianity).