Vatican City (AFP) - Uttering a centuries-old command, Pope Francis on Tuesday opened a "Holy Door" of St Peter's basilica to kick off an extraordinary Jubilee year, while urging his Church to reach out to the modern world.
"This is the door of the Lord. Open to me the gates of justice," the Argentinian pontiff said before being helped up three marble steps to push the giant bronze doors open.
In a break with tradition that reflected Francis's modernising instincts, the order to open the doors was delivered in Italian rather than Latin.
The 78-year-old then paused on the threshold of the Renaissance basilica for two minutes of silent prayer before walking inside in an act to be carried out by millions of pilgrims before the Jubilee - a special year of remission of sins and universal pardon - closes next November.
Francis was followed gingerly through the door by his frail predecessor, the now-retired Benedict XVI, 88, and by hundreds of cardinals, bishops and male and female members of religious orders.
Clutching a walking stick in his right hand and looking extremely pale, Benedict was helped into the basilica on the arm of his assistant Georg Ganswein.
Amid heightened security following recent terror attacks around the world, the Vatican said 70,000 pilgrims had packed into St Peter's Square and surrounding streets to watch Francis open the usually bricked-up portal of the Renaissance basilica.
Many had tears rolling down their cheeks or eyes clenched shut in prayer as Francis ordered the door open for the first time since the last Jubilee, in 2000.
Among them were Polish friends Teresa and Carolina, who were back in Rome after coming for John Paul II's Jubilee 15 years ago. "What will I change to mark the Jubilee? I think I'll give some change to a homeless beggar that I usually ignore," confided Teresa.
Francis used his homily to underline the significance of his decision to start the Jubilee on the 50th anniversary of the end of the Second Vatican Council, a gathering of bishops credited with a modernisation of the Church that Francis is attempting to emulate.
Tuesday also marked the 1,000th day of Francis' pontificate.
For Francis's predecessor, the German-born Joseph Ratzinger, Tuesday's ceremony was a rare public outing.
The Emeritus Pope, as he is officially known, has lived in seclusion within the Vatican since retiring in 2013 as failing health left him incapable of running an institution beset by the clerical sex abuse scandal and internecine bickering in its upper echelons.
Tuesday's celebrations were rounded off in the evening when images by some of the world's greatest environmental photographers including Brazil's Sebastiao Salgado and Yann Arthus-Bertrand of France were projected onto the facade and dome of Saint Peter's.
The giant, moving photos depicting environmental issues such as endangered species, desertification and overconsumption were an initiative linked to the ongoing COP21 global climate conference in Paris.
- Mercy not judgement -
Francis called the Jubilee, which runs until November 20, 2016, with the express goal of changing the way the Church is perceived by the faithful, lapsed believers and the rest of the world.
"How much wrong we do to God and his grace when we speak of sins being punished by his judgement before we speak of their being forgiven by his mercy," he said Tuesday.
"We have to put mercy before judgement... Let us set aside all fear and dread, for these do not befit men and women who are loved."
In a surprise move reflecting that aim, Francis announced in September that for the duration of the Jubilee, priests would be given special dispensation to absolve women who have had abortions.
In addition, some 800 priests around the world are to be designated "missionaries of mercy" tasked with encouraging higher levels of confession amongst believers.
Those involved have been selected for their ability to preach well, understand human frailty and ensure that the confessional is not experienced "like a torture chamber" as the pope has put it.
Francis's push for a less judgmental, more understanding Church has encountered 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.