Pope Benedict XVI begins his first state visit to France on Friday, hoping to strengthen President Nicolas Sarkozy's call for a more positive view of Christian values in Europe.
The leader of the world's one billion Catholics will be greeted by Sarkozy and his wife Carla Bruni when he arrives in Paris.
The 81-year-old pontiff will go to the Elysée palace for talks with Sarkozy, who caused a stir when he last year called for a “positive secularism” that would allow space for religion in public life.
While France is a predominantly Catholic nation, politically it strictly upholds the separation of religion and state.
Last year Sarkozy's comments that “religions should not be considered a danger, but an asset” were taken as an attack on the principal of separation.
France can uphold its Christian roots without compromising its commitment to secularism, said Sarkozy, a twice-divorced lapsed Catholic.
After leading services at an open-air mass in central Paris on Saturday, where crowds of around 250,000 are expected, the pope will fly to Lourdes.
There he will commemorate the 150th anniversary of the visions of Saint Bernadette - a village girl who claimed to see the Virgin Mary appear several times.
More than 200,000 people are expected to descend on the town where Bernadette Soubirous is said to have seen Mary 18 times over a period of a few months in 1858.
A fluent French speaker, Benedict said in a message earlier this week that he was coming to France as a “messenger of peace and fraternity.”
"Your country is known to me. Several times I have had the joy of going and appreciating its generous welcoming tradition, its tolerance and the strength of its Christian faith as well as its spiritual and human culture," he said.
The four-day visit to France will be Benedict's first since his election in 2005 following the death of John Paul II.
A survey published last year showed 51% of the French consider themselves Catholic, down from 80% in the early 1990s.
Of those, only 10% attend mass regularly, the survey in Le Monde des Religions magazine showed.
The pope ends his trip on Monday with a mass for the sick in Lourdes.
Some 9,200 police officers and gendarmes will be mobilised to ensure security during the visit.