Popes John Paul II and John XXIII have been declared saints at an historic ceremony at the Vatican, presided over by Pope Francis and in the presence of the retired Pope Benedict XVI.
Francis recited the saint-making formula in Latin, saying that after deliberating, consulting and praying for divine assistance "we declare and define Blessed John XXIII and John Paul II be saints and we enroll them among the saints, decreeing that they are to be venerated as such by the whole church."
Benedict was sitting off to the side with other cardinals in St Peter's Square during the rite at the start of Sunday's Mass. He and Francis briefly greeted one another after Francis arrived.
The squares and streets of the Vatican were packed with hundreds of thousands of people for the ceremony, with the overwhelming majority made up of Polish people who had made the pilgrimage to see their most famous compatriot, John Paul II, become a saint.
Hundreds of red and white Polish flags filled the square and the streets surrounding the Vatican, which were strewn with sleeping bags, backpacks and folding chairs. It was one of the biggest crowds since John Paul II's beatification in 2011.
John XXIII, who reigned from 1958 to 1963 and called the modernising Second Vatican Council, and John Paul II, the Pole who reigned for nearly 27 years, played a leading role on the world stage.
Francis' own huge popularity has added extra appeal to the unprecedented ceremony to raise two former leaders of the church to sainthood on the same day. But while both were widely revered, there has also been criticism that John Paul II, who only died nine years ago, has been canonised too quickly.
Groups representing victims of sexual abuse by Catholic priests also say he did not do enough to root out a scandal that emerged towards the end of his pontificate and which has hung over the church ever since.
On Friday, people claiming to be victims of sex abuse held a candle-lit vigil at the Vatican in protest at the canonisation, holding up pictures of children alleged to have been abused by priests.
In an open letter published on the website of the survivor’s network SNAP (the Survivors Network of those Abused by Priests), a number of victims highlighted the “great harm” committed as “he [John Paul II] turned a blind eye to “clergy sexual crimes and cover ups".
“At worst, he perpetuated and approved them,” the statement said. “For him to now be given the highest honor in the church rubs even more salt into the already deep and still fresh wounds of thousands of struggling victims and millions of betrayed Catholics and victims.”
Earlier this month, Pope Francis issued an apology for the scandal, asking for forgiveness for the "evil" damage done to children who were targeted by members of the clergy.
But the controversy did nothing to put off the rivers of Catholics who have been arriving in Rome over the past few days.
Around one million Catholics are reported to have turned out to celebrate the occasion across Rome, while pilgrims hoping to get into the Vatican itself had waited for more than 12 hours before police opened up the square at 5.30am this morning.
Alongside Francis at the mass were around 850 cardinals and 700 priests, helping to distribute communion to the vast crowd.
"For years Pope John Paul II took the Church to the ends of the earth and today the ends of the earth have come back here," said Father Tom Rosica, head of Canada's Salt and Light Catholic television network.
"Four popes in one ceremony is a fantastic thing to see and to be at, because it is history being written in our sight," said one of the visiting Poles, David Halfar. "It is wonderful to be a part in this and to live all of this," he said.
"It is a great joy, an immense joy, because there is happiness everywhere and this is not an empty happiness," said Guillemette Chevalier, from France.
"Here we have found the joy of being together in the Church around two extraordinary men ... who give meaning to our lives. It is true happiness," she said.