What is Proclamation of the Birth of Christ?

The Proclamation of the Birth of Christ, Kalenda Proclamation, or Christmas Proclamation, is a chant sung before the Midnight Mass for Christmas in the Roman Rite of the Catholic Church. The long text is a timeline, in which each verse represents the years from an historical event, either secular or religious, until birth of Jesus Christ, and the number of years – expressed in centuries or years – decreases until the day of the first Christmas.