(October 13, 2007)PARIS F From the outside, St.-Francois-Xavier Church just might be the ugliest church in Paris. A 19th-century hulk, it drips with decades of brownish-grey grime. There is not one memorable feature on its facade. Although the gold-domed Invalides with Napoleon’s Tomb is only a few blocks away, St.-Francois-Xavier stands on a loud, traffic-clogged intersection leading to the Montparnasse train station, facing some of the worst of recent Paris architecture.

But one Sunday morning, I find myself lurking in its vestibule, waiting for the 10:15 family mass to let out. Using head-bowing and tiptoeing rituals learned from the nuns of my childhood, I nudge my way through the departing faithful. Seeing no one in authority, I rush through a side door behind a gaggle of white-robed altar boys. There are no tourists here, and even the regular parishioners don’t stop by.

I have entered the church’s “wedding sacristy,” an unfurnished space that seems to have no other purpose than to store vestments in locked oak cupboards. The two stained-glass windows need cleaning, the parquet floor polishing, the walls a good paint job.

But there, framed in gold and hanging nonchalantly under slim fluorescent lights, is a 16th-century Last Supper by the Venetian painter Tintoretto. The only Tintoretto to hang in a Paris church, the painting found its way from Venice to this destination as a gift from a French baroness a century ago.

For a moment, the painting is mine.

Paris ordinarily defines itself to visitors as a city of museums, monuments, neighbourhoods and opportunities for shopping and eating. But there is another way into the history, culture and daily fabric of this city’s life, a voyage of discovery into a world overlooked even by Parisians themselves: its churches.

Seeing Paris through its churches — its “vast symphonies of stone,” to paraphrase one of Victor Hugo’s descriptions of his beloved Notre Dame — is to be thunderstruck. The surprises range from the hallucinatory (the intricately carved, lofted arch-screen of the 16th-century St.-Étienne-du-Mont Church next to the Pantheon) to the culinary (the basement stone crypt of the 17th-century Polish church Notre-Dame-de-l’Assomption that serves as a restaurant offering pickled herring and pork schnitzel.)

Churches are silent survivors, witnesses to successive upheavals in France. The most dramatic was the violent anticlericalism following France’s 1789 revolution that stripped churches of their riches, transforming them into “temples of reason” in the service of the new secular republic. Churches were razed; stained-glass windows broken; altarpieces and statues smashed; tombs emptied; church bells melted to make cannons; gold chalices sent to the mint.

The remains of St.-Geneviève housed in St.-Étienne-du-Mont were burned, as was the celebrated library of St.-Germain-des-Prés; St.-Joseph-des-Carmes was turned into a prison for insubordinate clerics who were massacred just outside. Notre Dame Cathedral was so badly defaced and desecrated that by the end of the 18th century, radicals called for its demolition.

Miraculously, many works of art were inventoried and carted away for safekeeping. Paintings were considered part of France’s heritage — not vile religious objects — and were largely spared destruction. So were the tombs of the French kings at the St.-Denis Basilica just outside the city limits.

When Napoleon rehabilitated the Catholic Church and it came time to return the objects, a high-stakes free-for-all followed as well connected and culturally savvy priests fought to secure the best objects for their own churches.

So how to start on this journey of discovery? It is easy — essential, really — for the first-time visitor to make pilgrimages to Notre Dame (the No. 1 tourist destination in town) and Sacre Coeur (No. 2), ahead of the Louvre (No. 3) and the Eiffel Tower (No. 4).

Deciding what else is worthy of discovery is harder, in part because there is no coherent unity to Paris churches.

They fall into distinct historic categories: medieval structures such as Ste.-Chapelle, one of the world’s most glorious examples of Gothic architecture; French Renaissance structures such as St.-Eustache near Les Halles, which blend imposing Gothic proportions with tiny classical details; 17th-century Baroque and Classical churches that sprang up with the expansion of Paris , such as the Jesuit showstopper of St.-Paul-St.-Louis; neo-Classical grand temples that came a century later including the Pantheon; and finally, the 19th-century wedding cake extravaganzas built with iron columns and girders like St.-Augustin, the product of Baron Haussmann’s 19th-century urban renewal that razed entire neighbourhoods, churches included.

Another challenge is that some of the more intriguing if little-known churches are unaccustomed to accommodating tourists. English-language tours that focus exclusively on churches are unreliable, so you have to love lonely wandering. Without an understanding of words like “chancel,” “rood” or “iconostasis,” guidebooks can seem impenetrable.

Many churches have only natural light so their moods change with the time of day. The painting of St. Étienne Preaching to the Angel in St.-Thomas-d’Aquin, an elegant, well-scrubbed structure hidden in a square off the rue du Bac, is luminous in the morning, dull in the afternoon. So is The Transfiguration on the ceiling above the altar, the only original decoration to remain after revolutionaries emptied the church of its treasures.

Visitors might head to St.-Sulpice in the chic part of the Sixth Arrondissement to see two paintings and a fresco by Eugene Delacroix and find them wrapped in darkness. A more striking — and better-lit — Delacroix (Christ in the Garden of Olive Trees) hangs above a doorway in St.-Paul-St.-Louis in the Marais on the other side of town.

Some churches are secret and unassuming, open only for weekend services or by appointment. My favourite is St.-Seraphin-de-Sarov, a Russian Orthodox Church on a working-class street in the 15th Arrondissement. Only a small plaque on a painted green door announces its presence behind a locked gate at the far end of a courtyard.

Visitors are invited to services on Saturday evenings and on Sundays, when coffee and tea are served in an overgrown, tranquil garden. Otherwise, the church can be visited by appointment with a painter who lives in a house on the site, and who will be happy to invite you in to look at his watercolours (all for sale).

Perhaps Paris’s most overlooked religious gem, given its size and importance, is the St.-Denis Basilica. In the working-class and lower-class suburb of St.-Denis outside of Paris, it’s easily reachable on Metro line No. 13 and a perfect outing on Sunday morning.

According to one legend, after St. Denis was decapitated near Montmartre during a persecution of Christians, he picked up his head, washed it off and carried it about five miles to the north before he collapsed. A shrine was built, replaced by the basilica, which became the place of burial for France’s kings from Clovis and Dagobert I to Louis XVIII (with royals like Catherine de Medici, Maria Theresa of Austria, Henri IV, Marie Antoinette and Louis XVI along the way).

Unlike Notre Dame, Paris’ star Gothic church that glitters from years of sandblasting, cleaning and polishing, much of St.-Denis’ Gothic facade hides behind black soot. I find its cool, pillared burial crypt the perfect place for children to play hide and seek (respectfully). Sculptural details delight: the feet of Blanche de Navarre resting on two dogs, those of Charles Comte de Valois on a lion.

Paris churches are static, beautiful museums, certainly; they are also vibrant parts of the everyday lives of their communities, places of music and ritual and prayer where infants are baptized, believers take Communion and the dead are mourned.

New York Times News Service