12 Days of Christmas

From Christmas to Epiphany used to be important, with saints' days celebrated, and pagan festivals adapted to Christianity, beginning with a day of charity on Good King Wenceslas' Feast of Stephen and ending with the day famous from Shakespeare as Twelfth Night. Read about the 12 Days in Christian History.
From Merry Christmas, sad Christianity:

"The adoption of what was the pagan Saturnalia festival of the Romans, with all its trappings, might prove to have been an ingenious and brilliant strategic move of the Roman church: i.e. successfully eclipsed the Saturnalia, known for its debaucheries and revelry, and imprinted on the world a festival which has proven the greatest boon for merchants all over the world."
"However, Christians are learning that the people of the world have been able to quite discreetly separate the religious elements from the essentially celebratory and festival elements of what has truly become a secular festival."

12 Days of Christmas Symbolism
Names of the Magi