Pilgrims from around the world flocked to the Vatican on Saturday to see Pope Benedict celebrate his first Christmas eve mass as leader of the world's 1.1 billion Roman Catholics.
The 78-year-old German Pontiff was due to say a mass in St Peter's Basilica for some 9,000 people.
Those who did not manage to obtain tickets, which are distributed free, will watch in the cold night air on giant screens in the square outside Christendom's largest church.
Thirty cardinals among those who elected Benedict last April 19 to succeed the late Pope John Paul II will join him in celebrating the mass from the basilica's main altar.
The celebration will be televised live to 46 countries and followed by tens of millions of people on television and radio.
In recent years, security around the Vatican has been tight, with nearly everyone entering the basilica having to pass through airport-style metal detectors and undergo bag searches.
Traditionally, popes keep their homilies at the Christmas midnight mass to the spiritual, recounting the story of the birth of Jesus in a stable in Bethlehem. But in the run-up to Christmas, Benedict has made it clear that he is increasingly worried about the commercialisation of season, lamenting that many had forgotten the real reason for the day - commemorating the birth of the Son of God.
At midday on Sunday, Benedict will read his first "Urbi et Orbi" (to the city and the world) Christmas message and blessing from the same central balcony of St Peter's where he first appeared to the world as Pope minutes after his election.
He is expected to speak about the state of the world and made an appeal for the peace in the Urbi et Orbi message, which is due to be televised live to nearly 40 countries.
On Saturday afternoon, workmen were due to unveil the life-size nativity scene which has been put up in the square alongside a 30-metre-high Christmas tree which this year was a gift of Austria. He also will say a mass on the Feast of the Epiphany on January 6, and two days later will baptise children. In early January, the Pope is due to publish his first encyclical, a major writing addressed to all Church members.