The tradition of the Posadas was brought to Mexico from Spain in the 1500's by Catholic Missionaries. The Posadas commemorate Mary and Joseph's difficult journey from Nazareth to Bethlehem in search of a place for the Christ Child to be born.
In Spanish, the word means dwelling or lodging. The Posadas begin on December 16 for nine evenings, culminating with the Posada on December 24 and Midnight Mass.