The late Pope, John Paul II, has been beatified at a ceremony at the Vatican in front of hundreds of thousands of Catholic faithful.
Among those at St Peter's Square is French nun Marie Simon-Pierre, who says she was cured of Parkinson's Disease.
Her apparently miraculous cure is part of the case for the beatification, the last stage before sainthood.
It comes amid criticism of the Church for the speed of the beatification and the clerical child sex abuse scandal.
Much of the abuse, or its alleged cover-up, occurred while John Paul II was Pope, from 1979-2005, and the Church has been criticised for not doing enough to punish those found responsible.
Police in Rome estimated that one million people had come to the city for the event, including large numbers of pilgrims from the late Pope's native Poland.
St Peter's Square, in the Vatican, was packed, with the faithful waving banners and flags as Pope Benedict XVI declared his predecessor blessed, or beatified.
Rome has not seen crowds of this size since the death of Pope John Paul II six years ago when some three million pilgrims converged on the Italian capital, says the BBC's Vatican correspondent David Willey.
Zimbabwean leader Robert Mugabe was among those attending the beatification.
A Roman Catholic, he was given special permission by the EU to fly to Italy despite being the subject of a travel ban.
The presidents of Poland and Mexico are also among some 90 heads of state and other dignitaries attending the beatification.
St Peter's Square was transformed for the occasion with a giant video screen showing Pope John Paul II's life story and a massive photograph hung from the white colonnades.
The late pontiff's coffin was exhumed from the crypt below St Peter's Basilica to be placed in front of the altar.
After the Mass, it will be moved to a different part of the basilica.
Some have questioned the Church's speed in beatifying the late Pope, just six years after his death.
Others have criticised John Paul II's handling of the Church's child sex abuse scandal.
"This sprint to sainthood is to deflect examinations into JPII's unedifying record on clerical child abuse - and, with it, Benedict's own role," said Keith Porteous Wood of Britain's National Secular Society.
Although John Paul II will be remembered as one of the great Popes of modern times, says our Vatican correspondent, the sex abuse scandal is the unspoken footnote of history.
The Vatican says he could not have been expected to do something about events he knew nothing of, but it is unlikely he was completely unaware of the growing scandal, our correspondent says.
'I was cured'
Beatification, or declaring a person to be "blessed", is the necessary prelude to full sainthood.
For this to happen, the Vatican must declare the person to have performed a miracle.
In John Paul II's case, Sister Marie, 49, said she and her fellow nuns had prayed for the intercession of the Pope after his death to cure her from Parkinson's Disease.
Her sudden cure had no logical medical explanation and she later resumed her work as a maternity nurse, the Vatican says.
Appearing at a vigil on Saturday, she told the crowd: "I was cured on the night between June 2 and June 3, 2005.
"I woke up at four in the morning and felt that something had changed in me."
If the late Pope is declared to have influenced another miracle he will be eligible for canonisation as a saint.
The vigil had the feel of a youth festival, correspondents say, with groups of young people dancing and singing. Many carried backpacks and sleeping bags in preparation for a night to be spent outdoors.
"It's true that nowadays most of the young don't care about religion, but John Paul showed us love, and love is all we need," said Matea Sarlija, a 21-year-old Croat, who had spent 10 hours on a bus to arrive in Rome for the vigil.