Afew weeks from now, at the break of dawn Saturday, May 30, more than 10,000 Catholics will gather on the public square in front of Notre Dame Cathedral in Paris.

As gray light spreads in the sky behind the famed spires, the air will crackle with youthful excitement, mixed, in the minds of the more realistic, with a touch of dread.

In the three days that follow, there will be much to suffer. But these Catholics know that their blood and sweat have infinite value, in the eyes of God.

These are the young people of France, primarily teenage boy and girl scouts, who walk every Pentecost between Paris and the famed Chartres Cathedral, reviving an ancient pilgrimage in a Catholic country that has, for the most part, renounced the Faith.

They are joined by several hundred foreign pilgrims, including, for the last two years as well as this year, myself. There is something mysterious about the experience that continues to draw me back.

We begin at 7:00 a.m. by marching into Notre Dame, behind colorful banners of long-dead saints. Each year, as we kneel for a blessing, there is a feeling that an epic battle is about to commence.

Then, we sing Veni Creator Spiritus, before turning to follow a statue of the Blessed Mother carried on the shoulders of four boy scouts. In the dark moments of the 70-mile walk, when blisters make every step painful, it helps to remember that she leads us.

More than 100 priests and seminarians are among the pilgrims. It's difficult to find one over the age of 40. All of them dress in cassocks, some wear birettas on their heads. Much of the march is across open fields or along rock-strewn muddy paths. Usually, it rains at least one day of the pilgrimage, and the afternoons grow hot. By the second day, the hems of their cassocks will be ragged. But they don't seem to mind.

The pilgrims sleep on the ground, in well-organized campsites. The diet consists mostly of bread and water, except for strong coffee each morning, ladled from steaming vats. Every day, High Mass is offered in the fields, with utmost reverence and sublime Gregorian Chant.

Along the way, family and friends join us, until the line swells to more than 16,000.

When we enter the walled city of Chartres, the bells peal in a wild welcome. Then, there is a three-hour pontifical High Mass, offered in the pre-Vatican II form.

The Holy Father sends his written greetings, and last year he sent a cardinal from the Vatican to offer the Mass. He seems eager to embrace these young people, most of whom attend traditional Latin Masses that are approved by their local bishops.

The cathedral has more than an acre of floor space, but it's not big enough to fit all the pilgrims. Thousands stand outside the doors, following the Mass via speakers, using the sound of the bells to keep pace as they kneel for the consecration.

Before receiving Communion, the pilgrims kneel and recite three times, striking their breasts, “Domine non sum dignus” (Lord, I am not worthy). Their young voices echo off the ancient stone walls, a moment that each year sends a shiver down my back.

Every joint will ache after our long walk. But the pilgrims receive Communion on their knees, with a boy scout holding a paten under their chins as a priest places the host on waiting tongues.

Then, at the end of Mass, as the statue of the Blessed Mother is carried away, we sing endless rounds of Chez Nous Soyez Reine, a French hymn of love for the Blessed Mother:

“Vous êtes notre MËre, Portez à votre Fils, La fervente priËre, De vos enfants chéris” (You are our Mother, Carry to your Son, The fervent prayer, Of your dear children).

Perhaps it's mere exhaustion, but even grown men weep as the end of the song nears, and, thus, the end of the pilgrimage is reached.

The Catholic Church survived a pogrom in the wake of the French Revolution. No matter how many sanctuaries were defiled, no matter how many priests and nuns were killed, the people clung to the Mass.

Today, being Catholic won't earn you a trip to the guillotine. But only about 10% of French Catholics attend Sunday Mass, and French culture is no longer Catholic. Quietly, modernism has done what violence could not achieve.

And, yet, amid the ruins, in a country once known as “the eldest daughter of the Church,” the faith lives on, as seen in the joyful faces of these young pilgrims.

Kathleen Howley is a Boston-based journalist.