Pope Francis will this week launch a Roman Catholic Jubilee dedicated to the theme of mercy against a backdrop of unprecedented security in and around the Vatican.
In the latest incarnation of a 700-year-old Catholic tradition, tomorrow will mark the beginning of a holy period of just under a year in which believers are encouraged to renew their relationship with God and seek forgiveness for their sins.
The jubilee runs until November 20, 2016. As has been the case for seven centuries, pilgrims visiting Rome will be able to mark the occasion by entering St Peter's and other famous churches through special holy doors that are kept bricked up between Jubilees.
But the pilgrimage is no longer a required rite. In a Francis innovation, believers will have access to holy doors around the world - including in the Central African Republic capital, where the pope himself opened a door last month.
Francis also set a new tone for this Jubilee with his surprise announcement in September that he would be granting every priest the discretion to absolve women who have had abortions.
It was a remarkable move for the leader of a church that views the termination of pregnancies as a heinous sin which, in normal times, is punishable by excommunication.
Pro-choice groups are sceptical about whether many women - or doctors who carry out abortions for that matter - will avail themselves of the pope's offer to confess.
Instead, many Vatican watchers saw the move as another example of Francis signalling his desire to change the church's approach from condemnation of wrongdoing to understanding of the difficulties posed by 21st century believers.
Jubilee years have their roots in an Old Testament tradition of freeing slaves and prisoners once every 50 years.
The concept died out in Judaism with the dispersal of Jews around the world but was relaunched in a Catholic format by Pope Boniface VIII in 1300 with pilgrimages to Rome at its heart.
They have been held variously at intervals of 25, 33 (Christ's age when he was crucified) and 50 years with occasional extraordinary ones slotted in between.
The last Jubilee was in 2000 and was called by John Paul II to mark the millennium.