Today in History—December 25: The Day Christmas Made the Calendar

On this day in 352, Pope Liberius celebrated the first official Christmas mass in Rome—marking the moment December 25 became the day on the calendar.

This wasn’t the first time Christians had celebrated Jesus’ birth: Some observances likely took place as early as the 2nd century, and the church in Rome began recognizing Christ’s birthday in 336. But it was Emperor Constantine’s legalization of Christianity two decades earlier that helped the church claim its place on the Roman calendar.

Pope Julius I is traditionally credited with confirming the date of Jesus’ birth—reportedly using census records (though some dispute remained over the date)—and assembling a basic church calendar of feast days of saints and martyrs—and Christmas. He died in April 352, so the honor to say the first calendar-codified “Christ’s Mass” fell to Pope Liberius.

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Why December 25? There are a few theories. The date lined up with popular pagan festivals, including the rebirth of the Unconquered Sun, which celebrated light’s triumph over darkness after the winter solstice, and Saturnalia, a mid-December week of revelry, mischief, and gift giving. The symbolism—and built-in audience—must have been hard to resist.

Early Christmas celebrations were bawdy affairs with plenty of pagan leftovers: drinking, singing, feasting, and presumably plenty of bad decisions. The endorsement of the church set Christmas on the path to becoming a religious affair, but some of the rowdier traditions (like wassailing and misrule) hung on, to the point where Christmas was actually banned in the mid-1600s in both England and Massachusetts.

That first official Christmas mass didn’t rein in the chaos, but fixing the date to the calendar gave it a purpose—and a liturgy. By the 9th century Christmas had become a major religious feast day. It continued to evolve, with decorated trees, Advent calendars, and gingerbread houses introduced as early as the 1600s in Europe. Immigrants brought these to America, and in the 1800s Christmas began to resemble the holiday we know today.

It would still take another century for Christmas to go full-on tinsel—a fittingly shiny evolution for a holiday born of bonfires.

Famous Birthdays

1665: Lady Grizel Baillie—Scottish poet

1821: Clara Barton—American humanitarian

1918: Anwar Sadat—Egyptian president

1971: Justin Trudeau—Canadian prime minister