Pope Benedict celebrated parts of Sunday's Mass with his back turned on the congregation, re-introducing an old ritual that had not been used in decades.

The Pope used the Sistine Chapel's ancient altar set right against the wall under Michelangelo's dramatic depiction of the Last Judgment, instead of the altar placed on a mobile platform that allowed his predecessor John Paul II to face the faithful.

A statement by the Vatican's office for liturgical celebrations said it had been decided to use the old altar, where ballots are placed during papal elections, to respect "the beauty and the harmony of this architectonic jewel".

That meant that for the first time in this kind of celebration since the Second Vatican Council (1962-65), the pope occasionally turned his back on the faithful and faced the Cross. He also read his homily from an old wooden throne on the left of the altar used by Pius IX in the 19th century.

The conservative German-born pontiff is slowly reintroducing some of the old rituals phased out after Vatican II, which substituted Latin for local languages, modernised the Church and encouraged inter-religious dialogue.

In July, the Pope issued a decree allowing wider use of the old Latin mass, in what was regarded as a nod to Church traditionalists. He has also said he would like the centuries-old Gregorian chant to make a comeback.

During Sunday's mass commemorating the baptism of Jesus Christ, which was celebrated in Italian, the Pope baptised 13 babies, carefully pouring water on their heads from a golden shell.

He spoke about the significance of baptism, which marks the admission of a person in the community of Christians.

Later at his weekly Angelus blessing, the Pope paid tribute to the World Day of Migrants and Refugees celebrated on Sunday, saying children who are born and brought up in refugee camps should be offered a different future.

But he also had a message for migrants around the world, telling them to respect the law and never give in to violence.