By THÉRÈSE MARGOLIS     

If you’re new to Mexico, you might have been surprised when, starting on around mid-December, your neighbors suddenly began banging on your door late at night demanding refuge and hot punch.

Those already familiar with Mexican Christmas traditions will recognize this unusual ritual as the official start of the holiday season.

La Posada – literally, the seeking of shelter – is Mexico’s unique way of ringing in the Christmas festivities, and the practice of going from door to door asking for safe haven is a symbolic reenactment of the journey Mary and Joseph made to Bethlehem in search of asylum from Herod, who had threatened to kill the first-born son of all who came from Nazareth.

Beginning exactly 10 days before Christmas and lasting through Dec. 24, the posada procession begins each night after dark, with small children – often dressed as angels – leading the way from house to house as friends and families recreate the pageant of the holy pilgrims.

The participants usually sings the “Litany of the Virgin,” a distinctive song in which the posada procession asks the owners of the house to grant them sanctuary “in the name of the heavens.”

The home owners then respond with a counter chorus, explaining that their home “is not an inn,” and refusing to open the door.

The musical recitation continues for several verses, and in the end, the hosts open their door and welcome the “pilgrims” in with a plate of cookies and a hot cup of punch.

On Christmas Eve, an additional verse is sometimes added to the litany, announcing that the time has come for Mary to give birth.

No one is quite certain as to how the posada tradition began in Mexico, but some sources attribute the custom to a 16th century Augustine order in the city of Puebla, that allegedly asked Pope Sixto V to grant them permission to host a nine-day Christmas celebration.

The Augustinians, who frequently used theater, drama and song in their conversion process, wanted to tell the story leading to Christ’s birth with a spectacular, hands-on ceremony that would convince the local Aztecs to accept Jesus as their savior.

By allowing the natives to reenact the procession of Mary and Joseph, the Augustinians hoped to personalize the story and capture the souls of the participants.

The nine-day procession also coincided with a pre-Columbian December festival dedicated to the war god Huitzilopochtli, and the plan was that a lively ceremony that culminated with song and food would be far more attractive to potential converts than a bloody ritual involving death and sacrifice.

Whether the Augustinian story of the birth of the posada tradition is true is a matter for historians to debate, but regardless of its origins, the posada is today a vital part of Mexican life.

Although modern society has sometimes morphed the posada into a less ritualistic open-house get-together, the idea that Christmas is a time to welcome guests and share celebrations is still very much ingrained in Mexican culture.