In the event, young French people descended on Paris in their hundreds of thousands, not to see a pop festival, or a sporting event, but to celebrate mass with the Pope at a race-course.
More than 500,000 young French people are estimated to have camped out at Longchamps overnight. They were joined by hundreds of thousands of young people who had come to the twelfth Catholic youth festival from 160 other countries. The congregation was put at 1,200,000, the largest audience for a religious occasion in France for more than half a century.
The French press and French commentators, both religious and secular, were busy yesterday trying to make sense of an event which appeared to stand many accepted facts about French youth on their head. The right- wing and Catholic Le Figaro said a "new generation of Christians" had been born. Even the secularist Le Monde asked whether this was the beginning of a "Longchamps" generation, who would be like the children of May 1968 in reverse: a generation seeking clear rules, firm morality and the leadership of the old.
Liberation, the centre-left newspaper which was itself born in the 1968 student revolt, declared that, like the doubting disciple Thomas, it had to accept the evidence of its eyes. The massive attendance at Longchamps had something important to say about France.
Laurent Joffrin, the newspaper's editor, said it was possible to minimise the event. "There is a Catholic genius for spectacle which has nothing to learn from rave parties, the Tour de France, or homosexual carnivals." The uniform of many of the pilgrims owed more to Bennetton than to the habits of monks or nuns.
But, all cynicism apart, he said, leftists must now accept that a large section of French youth felt alienated by the individualism and materialism of the modern world. They were turning not to politics, but to the social message of the Church, however much they might disapprove or ignore the Pope's teaching on contraception and abortion.
This is one interpretation. Judging by the vox pops and analyses in Liberation and other newspapers, the great majority of the "Longchamps generation" came from a more straightforward, right-wing French Catholic tradition. They were overwhelmingly provincial and well-heeled. Their transport had been mostly organised by Catholic schools, scout and youth groups. One man in his early 20s said: "I am the archetype of the provincial petit bourgeois Catholic. The Pope is my spiritual guide. Philippe de Villiers [the ultra conservative Catholic aristocrat who campaigned against Maastricht] is my political model."
None of this is to denigrate the scale and emotional impact of the event, which was followed by many millions of other French people on television. But it is important to place Longchamps in its context. By all the usual vital signs, Catholicism in France remains in slow but relentless decline. More than half of young French people say they have no religion and are indifferent to Christian culture. Religious vocations have collapsed. Ordinations of priests are down to fewer than 100 a year. Only 5 per cent of priests are less than 40 years old. Regular church-going is down to 17 per cent.
Many of those interviewed on Sunday admitted that they did not regularly go to mass. "In church, it's just the grey heads. Here, you feel in touch with something strong," said one 18-year-old girl.
Henri Tincq, writing in Le Monde, said the event had more than a flavour of US-style, Protestant evangelism, trading in simple emotion rather than profound feeling or contemplation. Several members of the French hierarchy said afterwards that they hoped the event would boost the number of religious vocations among the young. But Mr Tincq said "no-one should seriously believe" that all these youngsters in T-shirts were going to pour themselves into parish work and the structures of the Church.