Paris, France - Al Fath Mosque is in a scruffy immigrant neighborhood not far from the neon-lit kitsch of Pigalle. On Friday afternoons the mosque is jammed, and the overflow of worshipers--all men--spills into the streets.
Tourists who stumble on the scene reflexively reach for their cameras, struck by this unusual public manifestation of religiosity in a country where Christian belief has become passe.
In France and in almost every other European country, Christianity appears to be in a free fall. Although up to 88 percent of the French identify themselves as Roman Catholic, only about 5 percent go to church on most Sundays; 60 percent say they "never" or "practically never" go.
But Islam is a thriving force. The 12 million to 15 million Muslims who live in Europe make up less than 5 percent of the total population, but the vitality of their faith has led some experts to predict that Islam will become the continent's dominant faith.
Princeton University historian Bernard Lewis, the dean of American Middle East scholars, flatly predicts that Europe will be Islamic by the end of this century "at the very latest."
George Weigel, a leading American theologian, frets about "a Europe in which the muezzin summons the faithful to prayer from the central loggia of St. Peter's in Rome, while Notre Dame has been transformed into Hagia Sophia on the Seine--a great Christian church become an Islamic museum."
Lewis and Weigel represent a trend among American thinkers who say they fear Europe's doom if it does not re-Christianize, and soon. Most European experts believe those fears are exaggerated.
France, with Europe's largest Muslim population, surely will be a test case.
There is little argument about the severity of the crisis facing the Catholic Church in France. In contrast with the vigorous --and masculine--face that French Muslims present to the world, a typical Sunday mass almost anywhere in France will feature an elderly priest ministering to a dwindling congregation of mostly elderly women.
"Mass is boring," said Odon Vallet, a religion professor at the Sorbonne. "The ceremony isn't very beautiful; the music is bad; the sermon is uninteresting. Mass is for people who have nothing else to do on a Sunday--no sports, no hobbies, no shopping, no entertainment."
Islam, meanwhile, is France's fastest-growing religion. But this is mainly a result of immigration patterns, not conversions. Most of the 4.5 million Muslims who are about 7 percent of France's population are immigrants or the descendants of immigrants from former French colonies in North Africa and sub-Saharan Africa.
Global Islam is eager for converts. But in Europe, the situation is nuanced. According to Olivier Roy, a leading French scholar on Islam, Muslims in Europe would be happy for Christians to convert while Christians merely want Muslims to become more secular.
For Rachid, a 22-year-old Moroccan who smuggled himself into France a year ago, Al Fath Mosque offers a kind of surrogate family and support network in an unfamiliar land. Five times each day, he stops by to pray, fulfilling one of the most important duties of a Muslim.
"It helps me keep my Moroccan identity," said Rachid, whose last name is being withheld because he is in France illegally. "If I had to give up Islam to be French, I would never do it."
Although a few militant fundamentalists insist otherwise, most European Muslims say Islam is compatible with their life in the West.
Adel Remdannie, 28, a security guard at a department store, said he wants Islam to be seen as a "normal" religion. French-born of Algerian heritage, Remdannie prays at Al Fath "three or four times a week and on Friday always."
"People think Islam is dangerous. They see us [at Friday prayers] and they think we are extremists. But for us, praying is a normal thing. My parents go to prayers. I go to prayers. It is how we follow our religion," he said.
Despite the overflow at Al Fath, surveys suggest that the percentage of Muslims attending Friday prayers is not much higher than that of French Catholics who go to Sunday mass.
The image of jampacked mosques is a "trompe l'oeil," said Roy, the Islamic scholar. "You have many millions of square meters of churches in France, but only a few thousand square meters of mosques."
And even though the conversation in France these days is about the alleged difficulties of integrating and assimilating the Muslim community, Roy said French Muslims are becoming "Europeanized" in more ways than many suppose.
Birthrates among Muslims in Europe appear to be falling into line with a general decline across Europe, he said, and a majority of French Muslims describe themselves as secular or non-practicing. According to one survey, 64 percent said they did not practice.
While President Bush proudly declares America "a nation of prayer," French President Jacques Chirac praises the virtues of French secularism. France developed a distinctly French notion of church-state separation more than a century ago in an attempt to curb the influence of the Catholic Church. Known as laicite, it allows all faiths equal status and ensures that all are equally divorced from the functions of the state.
In recent months, laicite became the focus of renewed debate when it was used to justify a ban on Muslim head scarves and other conspicuous religious symbols in public schools and later to explain French opposition to the inclusion of any reference to Europe's Christian roots in the preamble of the new European constitution.
"France is a lay state, and as such she does not have a habit of calling for insertions of a religious nature into constitutional texts," Chirac explained.
Significantly, the EU constitution, stripped of all Christian references, was emphatically rejected by French voters.
Bruno Bourg-Broc, a deputy in the National Assembly, laments the erosion of the faith in France.
But, he says, "We are a fundamentally Christian society. The landscape is formed of churches. It's part of our culture, our literature and painting. Whether people want it [in the constitution] or not, we were formed in this way.
"The doctrine of Islam is to conquer and convert, and we must keep this in mind. I don't think there is a real risk here, but if it happens, it will be our own fault."
Last year, when Cardinal Joseph Ratzinger was elected pope and took the name Benedict, the patron saint of Europe, it was seen as a sign that he would refocus the church's energies on rebuilding the faith in Europe. The Vatican was heartened when a million young people turned out last August for World Youth Day in Cologne, Germany, and heard the new pope urge them to rediscover Europe's Christian roots.
Some experts also are encouraged on Christianity's behalf.
"If you are the type of person who buys stocks and bonds, I'd buy Christianity," said the Sorbonne's Vallet. "The price now is very low . . . it has to go up."
Other analysts believe Europe's future is neither Christianity nor Islam, but secularism. A pragmatic reading of the numbers suggests that not only will Christianity never regain its dominant cultural role, but churchgoers also will be forced to recast themselves as minority groups or subcultures.
"Who truly thinks that Benedict XVI is the future of Europe?" asked Roy. "Secularism is the future."