By Eric D. Huntsman, from Good Tidings of Great Joy, 89
A common way of commemorating the scene of Jesus’ birth is to set up a Nativity scene, also known as a crèche, from the Old French word for manger or crib. A crèche can be as simple as having figures of Joseph, Mary, and the baby Jesus in a manger. Shepherds are also usually added from the scene described by Luke 2, but other elements, such as the Wise Men and sometimes a star above the manger actually come from the later scene painted by Matthew 2. The stable itself and the various animals are imaginative but reasonable reconstructions, though ox and donkey are derived from Isaiah 1:3, and the camels for the Wise Men have their antecedents in a prophecy found in Isaiah 60:6, which was connected with the Wise Men because of its reference to their bringing gold and incense.
The earliest portrayal of the Nativity in art may be funerary paintings dating as early as A.D. 380 in the Roman catacombs of St. Sebastian and Priscilla. The practice of setting up a three-dimensional representation of the Nativity scene began with St. Francis of Assisi, who staged a living nativity scene in Greccio, Italy, in 1223. Using a peasant family and placing the baby in an actual hay-filled crib, St. Francis’ effort was meant to refocus Christmas celebrations on the actual humble birth of the Savior.
Although complete crèches are often set up in many homes early in the Christmas season, many churches are careful not to place the baby Jesus in the manger until Christmas Eve, and some do not introduce the Magi until January 6, the Feast of Epiphany, which in Western churches celebrates the arrival of the Wise Men.
 Bowler, “Crèche,” World Encyclopedia of Christmas, 53–54.