VATICAN CITY - Popes John Paul II and John XXIII will join the roster of saints at a historic Vatican ceremony on Sunday seen as an attempt to unite conservatives and reformists, with some 800,000 pilgrims expected in Rome.
The double canonisation of two of modern-day Catholicism's most influential figures will be presided over by Pope Francis and may be attended by his elderly predecessor Benedict XVI, bringing two living pontiffs together to celebrate two deceased predecessors.
Delegations from 54 countries are expected, including 24 heads of state, as well as hundreds of thousands from across the world who will be able to follow the ceremonies in different languages on 19 giant screens in some of the Italian capital's most picturesque spots.
Churches will remain open all night Saturday for prayer vigils ahead of the mass in St Peter's Square on Sunday to honour two Roman Catholic leaders whose pontificates spanned from the height of the Cold War with the Cuban missile crisis to the fall of the Berlin wall.
Tapestry portraits of the new saints will hang high above the crowds and thousands of bishops, priests, and scarlet-cloaked cardinals.
A piece of John XXIII's skin, taken when his body was exhumed for his beatification in 2000, will be on show, alongside a vial of John Paul II's blood.
The ceremony will be attended by Costa Rican Floribeth Mora, whose claim to have been healed from a brain aneurysm by praying for John Paul's intercession was accepted as one of the two "confirmed" miracles normally required for sainthood.
The pontiff, who reigned from 1978 to 2005, was credited with performing another miracle just six months after his death, when a French nun said she had been cured, through prayer, of Parkinson's - a debilitating disease from which he had also suffered.
Francis approved the canonisation of John XXIII (1958-1963) - with whom he shares a kindly demeanour and reformist views - based on just one supposed miraculous healing, saying that the late pope was so widely adored that he did not need a second one.
The unparallelled double ceremony is seen by Vatican watchers as an attempt to bridge a traditional left-right divide in the Church, but has drawn criticism from some who argue the canonisation process was rushed.
Though becoming a saint is usually an expensive and lengthy process that can take decades, John Paul II's elevation has been the fastest since the 18th century when the current canonisation rules were installed.