The 79-year-old pope, wearing a blue, red and gold cape over his white vestments, pushed open the door, then knelt in prayer on the stone floor for several minutes during the ceremony.
Two aides supported John Paul as he climbed the three steps leading to the door. At one point, he swayed backward, and Bishop Piero Marini put his hand on the pope's back to steady him.
After prelates recited prayers, African men sounded horns and women from Japan played notes on the koto to emphasize the universal reach of the church.
In his homily during the traditional midnight Mass that followed the ceremony, John Paul called the birth of Jesus Christ "the truth which on this night the church wants to pass on to the third millennium.''
``And may all of you who will come after us accept this truth, which has totally changed history,'' John Paul said, speaking in a clear voice.
He said Christ is the ``true door, symbolized by the door which on this night we have solemnly opened.''
Only 8,200 people can fit inside the basilica, so four giant TV screens were set up for the overflow. All 40,000 seats in the square were filled and tens of thousands more stood out on the damp night to witness the millennium event.
A global TV hookup broadcast the ceremony live to 58 countries, including Cuba, for those unable to come to Rome.
This is the 22nd Christmas Eve Mass that Pope John Paul II has celebrated here, reports CBS News Correspondent Lee Cowan, made even more special by the fact that he's declared this a holy Jubilee year. Vatican officials say he's determined to lead his flock through the year-long celebrations, which could mean a busy travel schedule, both here and abroad.
The pope has called for the faithful to mark the holy year by making a
pilgrimmage or other observance. Some 30 million are expected to come to Rome over the course of the year; that's more than six times the normal number who visit here.
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