When Pope Francis opens the Holy Door of St Peter's Basilica on Tuesday to start the Catholic Church's Jubilee on the theme of mercy, his predecessor Emeritus Pope Benedict XVI will be beside him.
Also attending the ceremony slated for 10.30 am are Italian president Sergio Mattarella, prime minister Matteo Renzi and a delegation from Italy's Muslim community, amid a massive security operation following last month's deadly Islamist terror attacks in Paris.
More than 2,500 soldiers are being deployed to assist police, street sellers have been barred from St Peter's Square and adjacent areas to the Vatican and transportation of arms, explosives, ammunition, fuel and toxic gases have been banned.
A no-fly zone will be enforced over the capital for the whole of the Jubilee, the Vatican and surrounding area is being monitored by a newly installed closed-circuit video system and Italian airforce radar and drones, while helicopters and fighter jets will be scrambled to intercept any suspicious airspace breaches.
Rome is expecting to welcome over 30 million pilgrims for the Jubilee during which believers are encouraged to renew their relationship with God and seek forgiveness for their sins, according to a 700-year-old tradition. The year of mercy runs until 30 November 2016.
Benedict, 88, stepped down from the helm of the Church in 2013, saying he lacked the physical and mental strength to continue leading more than 1.2 billion Catholics worldwide. He retained the title of emeritus pope and since he abdicated has lived in a converted monastery in the Vatican gardens, where he is said to spend much of his time reading and praying.