Pope John Paul II and Pope John XXIII are to be declared saints at an unprecedented open-air ceremony in Rome on Sunday.
A Mass co-celebrated by Pope Francis and his predecessor, Pope Emeritus Benedict, will be witnessed by one million pilgrims and a vast TV and radio audience.
Nearly 100 foreign delegations are due, including royal dignitaries and heads of state and government.
It is the first time two popes have been canonized at the same time.
Correspondents say the move is being seen as an attempt to unite conservative and reformist camps within the Roman Catholic Church.
Pope John Paul II and Pope John XXIII are to be declared saints at an unprecedented open-air ceremony in Rome
Pilgrims have been pouring into Rome and special bus, train and boat services ferried many more into the city early on Sunday morning for the two-hour ceremony which starts at 10:00 local.
Some had bagged places to sleep overnight as close as possible to St Peter’s Square, hoping to be among the first in when it opens to the public.
Giant screens have also been erected in nearby streets and elsewhere in the city for those unable to get into the square.
The Vatican confirmed on Saturday that 87-year-old Pope Emeritus Benedict XVI would make a rare public appearance alongside his successor, Pope Francis.
“He will co-celebrate, which does not mean he will go to the altar,” a Vatican spokesman said.
“We will all be happy to have him there.”
Benedict XVI became the first pope to resign for 600 years when he quit for health reasons a year ago, sending shock waves around the world.
The process of saint-making is usually long and very costly.
However, John Paul II, whose 26-year reign ended in 2005, has been fast-tracked to sainthood in just nine years.
Many among the huge crowds that gathered as he lay dying cried out “Santo subito!” (Make him a saint immediately!).
By contrast Italian-born John XXIII, known as the Good Pope after his 1958-1963 papacy, had his promotion to full sainthood decided suddenly and very recently by Pope Francis.
By canonizing both John XXIII – the pope who set off the reform movement – and John Paul II – the pope who applied the brakes – Pope Francis has skillfully deflected any possible criticism that he could be taking sides.
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Vatican officials announced today that Pope Benedict XVI will be known as “pope emeritus” and will retain the honorific “His Holiness” after he abdicates on Thursday.
He will also continue to be known by his papal title of Benedict XVI, rather than reverting to Josef Ratzinger.
Pope Benedict will wear his distinctive white cassock without any cape or trimmings.
He will surrender his gold ring of office, known as the fisherman’s ring, and his personal seal will be destroyed in the same way as when a pope dies.
Benedict XVI will also give up wearing his specially-made red leather loafers, instead wearing brown shoes hand made for him by a Mexican craftsman during a brief visit to Mexico last year, Vatican spokesman Federico Lombardi said on Tuesday.
His resignation is the first by a pope for some 600 years.
The title “emeritus” is used when a person of status, such as a professor or bishop, hands over their position so their former rank can be retained in their title.
The Pope is to spend his final hours at his Vatican residence saying farewell to the cardinals who have been his closest aides during his eight-year pontificate.
His personal archive of documents will be packed up and, at 20:00 on Thursday, the Swiss Guard on duty at his Castel Gandolfo residence will be dismissed, to be replaced by Vatican police.
Vatican officials announced today that Pope Benedict XVI will be known as “pope emeritus” and will retain the honorific “His Holiness” after he abdicates on Thursday
This will mark the formal end of his papacy and the beginning of the period of transition to his successor, due to be chosen next month.
From March 4, the College of Cardinals will meet in general congregations to discuss the problems facing the Church and set a date for the start of the secret election – or conclave to elect Pope Benedict’s successor.
That successor will be chosen by 115 cardinal-electors (those younger than 80 years old) through ballots held in the Vatican’s Sistine Chapel.
A two-thirds-plus-one vote majority is required. Sixty-seven of the electors were appointed by Benedict XVI, and the remainder by his predecessor John Paul II.
About half the cardinal-electors (60) are European – 21 of those being Italian – and many have worked for the administrative body of the Church, the Curia, in Rome.