Natalis dies

The Egyptian gnostics anyhow had the feast and set it on January 6, a day of the blessing of the Nile. It was a feast of Adoptionist complexion, as one of its names, viz. the Birthday (Greek -yev0Xta, Latin Natalicia or Natalis dies), implies. This explains why in east and west the feast of the physical Birth was for a time associated with it; and to justify this association it was suggested that Jesus was baptized just on His thirtieth birthday http://www.1911encyclopedia.org/Feast_of_Epiphany.