(CNN)This week is Holy Week, when millions of Western Christians mark the death and resurrection of Jesus. Under normal circumstances, Notre Dame Cathedral in Paris would have been preparing to display its holy relics to the faithful on Good Friday.
But as fire engulfed the sacred site on Monday, Catholics across the world reacted in horror and disbelief, particularly when the cathedral's iconic spire toppled amid the flames.
For generations, Notre Dame has been a place of pilgrimage and prayer, and, even as religion in France has declined for decades, it remained the beating heart of French Catholicism, open every day for Mass.
"I can't even look at it," the Rev. James Martin, a Jesuit writer based in New York, said of the televised images of flames devouring the cathedral's iconic Gothic architecture.
"Outside of St. Peter's Basilica (in Vatican City) I don't think there's a more iconic church for Catholics. I don't think there are any Catholics who visit Paris and don't pray or go to Mass at Notre Dame."
For Martin, as for other Catholics, it was difficult not to see several layers of symbolism in the flames: The fire broke out during Holy Week, the most sacred time on the Christian calendar, at a time when the Catholic Church worldwide is engulfed in controversy over the abuse of children, and when France has seen months of public anger over rising fuel prices.
Martin wasn't alone in his grief. As news of the fire spread Monday, many prominent Catholics expressed deep sadness.
"I just went next door to our own beloved Cathedral, Saint Patrick's, to ask the intercession of Notre Dame, our Lady, for the Cathedral at the heart of Paris, and of civilization, now in flames!" Cardinal Timothy Dolan of New York tweeted. "God preserve this splendid house of prayer, and protect those battling the blaze."
Cardinal Daniel DiNardo of Houston, president of the U.S. Conference of Catholic Bishops, called the fire "shocking" and saddening. But, like many Catholics, DiNardo connected the heartbreaking news to the coming Easter holy day.
"We are a people of hope and of the resurrection, and as devastating as this fire is, I know that the faith and love embodied by this magnificent Cathedral will grow stronger in the hearts of all Christians."
DiNardo said Notre Dame is more than the sum of its tumultuous history. The cathedral, he said, "has long been a symbol of the transcendent human spirit as well as our longing for God."
Cardinal Vincent Nichols, Archbishop of Westminster in England, called the cathedral "the heart of the faith" in Europe.
"Who is not deeply moved at the sight of this great Cathedral in flames?" Nichols tweeted. For the people of Paris this is a disaster that touches their very soul."
Good Friday
Notre Dame is not a parish church, meaning that it does not have a regular body of worshippers who "belong" to the church. But it is still the home church of Paris' Archbishop Michel Aupetit and draws Catholics for vespers (evening prayers) Masses and the Sacrament of Reconciliation, also known as Penance.
And every year during Holy Week, Notre Dame unveils some of the most coveted relics in Christendom. Among them is the Holy Crown, believed by many to be from the crown of thorns placed on the head of Jesus, and which the cathedral calls its "the most precious and most venerated relic." Catholics have prayed with the Holy Crown for more than 16 centuries, according to the cathedral.
Notre Dame also counts among its treasures two other relics connected to Holy Week: a fragment of the Wood of the Cross, believed by many to be a part of the "true cross" on which Jesus was crucified; and one of the nails that the Romans used to crucify Jesus.
That nail comes from the Holy Sepulcher, the place where Jesus was buried in Jerusalem, according to Notre Dame. Christians in Jerusalem gave the relic to the Emperor Charlemagne in 799, and it subsequently became a powerful object of veneration for generations of French Catholics.
During the French Revolution, when French secularists destroyed many iconic Catholic pieces of history and art, it was saved and given to the archbishop of Paris, according to the cathedral.
On Monday, as firefighters battled flames at Notre Dame, the safety of the relics was unknown.
As the flames rage Archbishop Michel Aupetit of Paris, whose home church is the cathedral, issued a plea for his priests to pray.
"The firefighters of Paris are still fighting to save the towers of Notre-Dame de Paris. The frame, the roof, and the spire are consumed. Let us pray. If you wish, you can ring the bells of your churches to invite prayer."
