Does anyone know the details about when the 12 days were added to the calendar (by whose authority?), which started the old folk-ways custom of celebrating Christmas on January 6th? I heard about this, partly because of the Christmas song "The Cherry Tree Carol", where the Christ, in Mary's womb, declares that "the sixth day of January my birtday will be," and from hearing Jean Ritchie talk about an old lady (her grandmother?) celebrating "Old Christmas." Is this also where the "Twelve Days of Christmas" comes from?