VATICAN CITY (AFP) - Uttering a centuries-old command, Pope Francis opened a "Holy Door" of St Peter's basilica on Tuesday (Dec 8) to kick off an extraordinary Jubilee year on the theme of mercy.
After celebrating mass in St Peter's Square, the leader of the world's 1.2 billion Catholics pronounced the words "open to me the gates of justice" in Italian - and pushed opened the heavy bronze door, which is normally bricked up.
Having previously greeted his predecessor Pope Emeritus Benedict XVI, 88, in the square, Francis led him and a procession of other prelates through the massive portal.
It was a rare public outing for the frail German former pope, who lives in near total seclusion inside the Vatican. His last appearance was for the canonisation of former popes John Paul II and John XXIII in April 2014.
Some 50,000 people were on hand for the latest enactment of the 700-year-old tradition laden with religious symbolism and beamed live around the world.
In Catholic tradition, the opening of "Holy Doors" in Rome symbolises an invitation from the Church to believers to enter into a renewed relationship with God.
The crowd included hundreds of cardinals, bishops and members of religious orders, attending under unprecedented security in the wake of recent terrorist attacks around the world.
As the mass began, many pilgrims had tears running down their cheeks, while others listened in silent contemplation or private prayer.
In the evening, images by some of the world's greatest environmental photographers were projected onto the facade of Saint Peter's in an initiative linked to the ongoing COP21 global climate conference in Paris.
The Jubilee, which runs until Nov 20, 2016, was called by the pontiff with the express goal of allowing the Church to "make more evident its mission to be a witness of mercy".
The pontiff has made the idea of mercy the dominant theme of his papacy, insisting that it is not simply an abstract concept.
In a surprise move, he announced in Sept that for the duration of the Jubilee, priests would be given special dispensation to absolve women who have had abortions.
Some 800 priests around the world are to be designated "missionaries of mercy" tasked with encouraging higher levels of confession among believers. They were selected for their ability to preach well, understand human frailty and ensure that the confessional is not experienced "like a torture chamber" as Francis himself put it.
Behind all this lies Francis's mission to make the Church seem less judgemental and more understanding, at times in the teeth of fierce resistance from traditionalists opposed to any relaxation of teaching on hot-button subjects such as homosexuality, divorce and unmarried cohabitation.
Traditionally, Catholics were expected to make a pilgrimage to Rome to benefit from the indulgences on offer to the faithful who pass through the Holy Doors during Jubilee years.
Francis has effectively done away with this custom by ordering cathedrals around the world to open their own Holy Doors. That will happen on Sunday, when Francis himself opens the door at one of Rome's major churches, St John Lateran.
With millions of pilgrims packing the already crowded streets of Rome, the city is jittery over potential attacks and security forces have been placed on high alert for the duration of the Jubilee.
"There has been no specific threat but the context is troubling," said Rome prefect Franco Gabrielli, the official in charge of ensuring the Jubilee passes off smoothly.