Under the noonday sun, I was scrambling up a rugged mountain trail toward four stone towers called the Châteaux de Lastours, each one perched on a perilous crag, when it struck me that I should have had more than a croissant and café au lait for breakfast. Of course, access was never meant to be easy.

Eight hundred years ago, these castles in Languedoc, a region of vineyards and olive groves that stretches from the Mediterranean to the Pyrenees in the southwest corner of France, were hideouts of the Cathars, a zealous religious sect that denounced many basic tenets of the Catholic Church. Pope Innocent III was alarmed by the Cathars' growing popularity, so in 1208 he declared a crusade to eradicate them.

Waves of cross-bearing warriors from northern France and Germany obeyed the holy call, laying siege to Cathar strongholds, slaughtering the heretics and pillaging their lands with a savagery that was startling even by the standards of the Middle Ages. In Béziers, at the northern edge of resistance, over 15,000 men, women and children - the entire population of the town as well as hordes of hapless refugees - were butchered. (The crusader monk Armond Amaury famously told his troops, when asked whom to spare, "Kill them all, God will know his own.")

Here at the isolated Lastours castles, which were built along a defensive cliff spur, the Cathars spent much of 1209 heroically fending off the onslaught. So the crusader leader, the sadistic Simon de Montfort, resorted to primitive psychological warfare. He ordered his troops to gouge out the eyes of 100 luckless prisoners, cut off their noses and lips, then send them back to the towers led by a prisoner with one remaining eye.

This macabre parade only hardened the Cathars' resistance, and they lasted until 1211 before capitulating. One by one, the other Cathar towns and strongholds fell to the sword. By 1229 the heresy was largely crushed, and the semi-independent counties of Languedoc, which had harbored it, had succumbed to French rule.

Dramatic stuff, you might say, but it's hard to visualize these grisly images when surrounded by such seductive mountain scenery. How could this frenzied cruelty have occurred under the same pearly blue sky where the breeze brings the perfume of wildflowers? The main Cathar sites of Languedoc are now part of the 10,570-square-mile modern French region of Languedoc-Roussillon, whose spectacular gorges, rivers, forests and thermal springs make it today one of the country's most popular summer destinations - a place where Parisians can be found hiking, swimming and savoring the excellent wine. In fact, on a sunny day, it comes as no surprise to learn that, at the same time as the crusade, Languedoc's many troubadours were creating some of the most enduring love poetry of the Middle Ages.

After a 15-minute climb along the exposed hillside, I clambered inside each of the four stark castles of Lastours, which lie about 100 yards apart and have been rebuilt and restored. I made my way up spiral stone staircases and peered through ancient arrow slits and ceiling gaps - nicknamed murder holes - through which defenders dropped rocks and poured boiling oil.

And yet (perhaps like the happy troubadours) my mind too began to wander from the tragic Cathar saga to more immediate sensual pleasures. I couldn't help remembering that in the tidy village of Lastours, where the steep trail had begun and where I had parked my car some 900 feet below, a very promising cafe had been putting out tables on a terrace beside the burbling River Orbiel. Instead of concentrating on medieval war crimes, I flashed back to the cafe's blackboard, which reminded me that there was a fresh salad Niçoise in the offing. And so, surrendering to the inevitable, I tumbled back down the trail to this cafe, which turned out to be a casual annex of a renowned Michelin-starred restaurant called Le Puits du Trésor - more promising still.

As I took my first sip of crisp white Vin de Pays d'Oc, I did feel a twinge of guilt for the valiant heretics, many of whom were devoutly austere. The Cathars believed that the world had been created by a force of darkness and heaven by God, and that all earthly activity was tainted and sinful. Aspiring only to the purity of early Christianity, they were appalled by the worldliness of the medieval papacy and its debauched clerics.

BUT as my appetizer of baked chèvre arrived, I reminded myself that even some of the top-ranking Cathar holy men, known as "pure ones" or "Perfects," were not entirely immune to Languedoc's less spiritual attractions. The historian René Weis records how two Cathar sages called the Authié brothers had a fondness for exotic spices, as well as fish terrines, local cheeses, honeys and "good wine." One of their hosts, concealing the brothers in his home from the Inquisition, set up to hunt down and purge the remaining Cathars, went forth "in search of a better and more renowned wine than the one he kept in his own residence," at considerable personal risk. This was still the Mediterranean, after all.

Today, you could never accuse the good people of Languedoc of hiding their heretic heritage. "You are in Cathar Country" proudly blares a sign on the busy highway from Avignon, followed by concrete statues of Cathar knights.

The romantic castles, superbly positioned on mountain peaks that can now be reached by car, have almost all been lovingly salvaged and adorned with lavish visitor centers, daily re-enactments of medieval life and light-and-sound shows. There is a roughly 150-mile hiking trail that links the key sites, called the Cathar Way, and another following the routes that fleeing heretics took through the backcountry.

I realized that there was more to this than just bringing in tourist euros when I saw a series of graphic novels for kids called "I Am Cathar!"

While the theological basis of their fight is alien to most of us today, the Cathars maintain a heroic aura for holding out as long as they did against overwhelming odds. For over a century after the official defeat, the survivors behaved like resistance fighters against the Inquisition, hiding out in the countryside and smuggling Cathar holy men from barn to barn. And quite apart from their underdog appeal, there is something compelling about their self-denial, which often led Cathars to choose being burned at the stake rather than renounce their faith. In the words of the French historian Emmanuel Le Roy Ladurie, Cartharism is like a dead star, which, after an eclipse of many centuries, again gives off "a cold and fascinating light ..."

My plan was to take a weeklong road trip through Languedoc toward the rugged border with Spain, to get to the heart of this medieval epic.

Unfortunately, my chances of imagining the historical drama seemed remote at my first stop, the town of Carcassonne, the famous gateway to Cathar Country, which manages to be both wildly spectacular and hopelessly cheesy. The first vision of its fairy tale fortress, La Cité, takes your breath away: Its enormous double ramparts, hovering on a hillside above the town, have 52 towers, each one crowned with fantastical "witch hat" turrets. These were actually added during Carcassonne's restoration in the 19th-century Gothic revival, but the effect is magical - from a distance. The down side to all this splendor strikes you when you enter the imposing fortress on foot, having parked your car in the vast lot or the Ville Basse, the Lower Town, where almost all of the 45,000 inhabitants live today. Carcassonne is now one of Europe's most popular tourist sites, and a tide of visitors is continuously pressing over the drawbridge into La Cité's only entrance, then squeezing into the even narrower Rue Cros Mayrevieille, where rows of souvenir shops sell Lord of the Rings daggers, wooden halberds and plastic helmets, like an endless Gothic Halloween store. Still elbowing through the crowds past a torture museum and haunted house, I started to feel like I was in Duloc, the "perfect" medieval town of "Shrek."

Clearly, one has to attack the fortress outside peak hours. I found a room in the heart of La Cité, so that I could explore its winding alleyways when the crowds had all but disappeared. Now more than a day-tripper, I set off in the silence of early morning to peer at the stone portraits that line the balustrades of the Basilica of St.-Nazaire, which dominates the southern edge of the fortress - each 13th-century face extraordinarily alive.

I even got over my aversion to the live jousting show performed several times every day, which at first (for obvious reasons) seemed very Medieval Times. It turned out that everything involved in the event had an authentic air, right down to the falconer advertising the event with his battered face, straggly long hair and 13th-century dentistry. The performance itself maintained an edge of danger, with the horsemen throwbacks to a more macho age.

Still, the true allure of the heretic trail lies outside Carcassonne. I soon realized that the fortress was the last reminder of the sunny, gentle postcard south of France of lavender fields and quaint B & Bs.

As I drove south into the mountains, the atmosphere grew more brooding, the temperature cooler and the tourists fewer with every mile. Even the people became different, their faces more closed, their eyes more suspicious, their accents thicker. (The name Languedoc refers to the Occitan dialect, where people say "oc" instead of "oui.") In the foothills of the Pyrenees, narrow roads meander along thousand-foot cliffs and stunning gorges. Side routes lead to half-deserted villages, ruined abbeys and ancient vineyards that produce a quaffable sparkling wine called blanquette de Limoux. After a couple of nights in the atmospheric spa town of Alet-les-Bains, where the tradition of taking the waters is alive and well and every cafe serves an excellent cassoulet, Languedoc started to feel like a quieter, more haunted cousin of Provence.

In this rugged Cathar heartland, nature itself sets your historical imagination working. After hours of white-knuckle hairpin turns, I arrived at the vertiginous Château de Peyrepertuse at the same time as an apocalyptic thunderstorm. I had to cower with a few other visitors while lightning bolts crackled for an hour, before we were allowed to clamber up to the fortress, which icy fogs had all but concealed.
Languedoc-Roussillon Travel Guide

Just as memorable was Montségur, some 40 miles west along winding mountain roads, the most forbidding of the Cathar fortresses, and the last to fall after a renewed spasm of rebellion in 1244. It sits on a fist of limestone at 3,000 feet, rising like some Machu Picchu of the Pyrenees; even the massive cut stonework seems to evoke Inca masonry. At these heights, tourists simply disappear in bad weather. During another torrential downpour I found myself alone on the steep trail leading up to the fortress. Through the mist and the sound of my own gasping breath, I could picture the crusader armies camped far below, 10,000 heavily armored troops starving the small citadel into submission. Today, fresh flowers are still placed around a memorial to the last defenders of Montségur, who were given the choice to convert or be burned alive; some 200 chose the latter. A museum in the village displays the skeletons of two Cathars. They were found by archaeologists, with arrowheads embedded in the bones, presumably killed while trying to escape.

Despite crusader victories, the Cathar heresy lingered subversively for about a century, eluding the most ruthless efforts of the Inquisition. The last bastion of the heresy was a village called Montaillou, hidden in the mountains south of Montségur, which has earned outsized fame among history lovers. In 1308, the Inquisition's officers arrested all 250 adults in the village, beginning a grueling series of investigations that would force the villagers to confess their most intimate secrets. The original Inquisition documents were discovered centuries later in the Vatican archives, and have proved to be a unique trove of information about everyday life in the Middle Ages.

Emmanuel Le Roy Ladurie used the material in his groundbreaking work of social history, "Montaillou," first published in 1975. The fascinating medieval soap opera, filled with lecherous priests, adulterous chatelaines and conniving peasants, became an international bestseller, adding a colorful new dimension to our pale vision of the medieval world.

Montaillou would be my final stop. But while the outpost looms large on the historian's world map, I had a hard time finding it near the remote border with Spain and Andorra. Finally, driving through rolling green pastureland, I spied the village near the Ariège River, crowned by an exquisitely decrepit tower of honey-colored stone. As I got out of the car, the only sound was the tinkling of water from a trough.

Somnolent it may be, but Montaillou has come back from the brink of nonexistence. Twenty years ago, it had only 10 permanent inhabitants; today it has 37, and a summer population nearly 10 times that. The Cathars have actually saved the village. "In the early 1990s, Montaillou was virtually a ghost town," said the mayor, Jean Clergue, who was born here and is an descendant of the same Clergues clan that dominated the area in the Middle Ages.

"But because of Le Roy Ladurie's book, everyone in France came to hear of it," he continued. "So when I moved back here in 1992, I met some friends and we said, 'We have to do something or this village is going to disappear!' " Mr. Clergue and several others first formed a group called Castellet to salvage the crumbling castle, promote archaeological excavations and hold historical festivals. Today, there is a store selling handicrafts, houses for summer guests and a small restaurant that opens in summer. There is even a radio station, Radio Montaillou.

Its castle may not be as imposing as others, but Montaillou is a strangely affecting place, perhaps because it is still alive; you could almost imagine that the few remaining villagers were the last of the Cathars. I strolled through the site of the original medieval village and followed an ancient trail to a lookout called the Col de Balagues. I was suddenly on the roof of Europe, gazing out at a jagged line of the Pyrenees to the south.

Cathar Perfects had used this same trail to elude the Inquisition, usually at night, often through blizzards. Of course, despite so much self-sacrifice, the heretics were doomed. Languedoc's last known Perfect was trapped and burned in 1321. But the brutality was almost too much to take in. I turned around and headed back to the village, where I'd noticed the only restaurant was advertising coq au vin for lunch.