On the development of the feast of Epiphany (which means “appearance” or “manifestation”), and the relative place of the Nativity, the baptism of Jesus, the miracle at Cana and the arrival of the magi as celebrated on this day, see Thomas Talley, The Origins of the Liturgical Year (New York: Pueblo, 1986), pp. 144–147, in which Talley shows that the development of January 6 as a celebration of the visit of the magi emerges when the date of the Feast of the Nativity is firmly established as December 25 (rather than January 6), and generally should be dated no earlier than the late fourth century. The Latin-speaking West shows this development earlier than the Greek or Syriac-speaking East, as shown by Augustine’s sermons and Prudentius’s hymn written for the feast of the Epiphany. See Augustine, Sermons 199, 200, 201, 202, 203 and 204; Prudentius, Hymn 12.

The determination of the 12 days between Jesus’ birth and the magi’s arrival in Bethlehem was most likely due to the reconciliation of the two different dates for Christmas in the first centuries (December 25 and January 6). Still, not everyone agreed, and different calculations remained. For instance, see Epiphanius of Salamis, Panarion 51.22.17, who not only argues that the magi took two years to arrive, but that they arrived on what he claimed to be the “very day of Epiphany”—the eighth day before the Ides of January, or 13 days after the increase of daylight (probably January 6 or 7, depending on which calendar he was using).