The Cathars were a religious group who appeared in Europe in the eleventh century, their origins something of a mystery though there is reason to believe their ideas came from Persia or the Byzantine Empire, by way of the Balkans and Northern Italy. Records from the Roman Catholic Church mention them under various names and in various places. Catholic theologians debated with themselves for centuries whether Cathars were Christian heretics or whether they were not Christians at all. The question is apparently still open. Roman Catholics still refer to Cathar belief as "the Great Heresy" though the official Catholic position is that Catharism is not Christian at all.

The religion flourished in an area often referred to as the Languedoc, broadly bordered by the Mediterranean Sea, the Pyrenees, and the rivers Garonne, Tarn and Rhône - and corresponding to the new French region of Occitanie (or the old French regions of Languedoc-Roussillon and Midi-Pyrénées)

As Dualists, Cathars believed in two principles, a good god and his evil adversary (much like God and Satan of mainstream Christianity). The good principle had created everything immaterial (good, permanent, immutable) while the bad principle had created everything material (bad, temporary, perishable). Cathars called themselves simply Christians; their neighbours distinguished them as "Good Christians". The Catholic Church called them Albigenses, or less frequently. Cathars.

Cathars maintained a Church hierarchy and practiced a range of ceremonies, but rejected any idea of priesthood or the use of church buildings. They divided into ordinary believers who led ordinary medieval lives and an inner Elect of Parfaits (men) and Parfaites (women) who led extremely ascetic lives yet still worked for their living - generally in itinerant manual trades like weaving. Cathars believed in reincarnation and refused to eat meat or other animal products. They were strict about biblical injunctions - notably those about living in poverty, not telling lies, not killing and not swearing oaths.

Basic Cathar Tenets led to some surprising logical implications. For example they largely regarded men and women as equals, and had no doctrinal objection to contraception, euthanasia or suicide. In some respects the Cathar and Catholic Churches were polar opposites. For example the Cathar Church taught that all non-procreative sex was better than any procreative sex. The Catholic Church taught - as it still teaches - exactly the opposite. Both positions produced interesting results. Following their tenet, Catholics concluded that masturbation was a far greater sin than rape (as mediaeval penitentials confirm). Following their principles, Cathars could deduce that sexual intercourse between man and wife was more culpable than homosexual sex. (Catholic propaganda on this supposed Cathar proclivity gave us the word bugger, from Bougre, one of the many names for medieval Gnostic Dualists)

In the Languedoc, known at the time for its high culture, tolerance and liberalism, the Cathar religion took root and gained more and more adherents during the twelfth century. By the early thirteenth century Catharism was probably the majority religion in the area. Many Catholic texts refer to the danger of it replacing Catholicism completely.

Catharism was supported or at least tolerated by the nobility as well as the common people. This was yet another annoyance to the Roman Church which considered the feudal system to be divinely ordained as the Natural Order (Cathars disliked the feudal system because it depended on oath taking). In open debates with leading Catholic theologians Cathars seem to have come out on top. This was embarrassing for the Roman Church, not least because they had fielded the best professional preachers in Europe against what they saw as a collection of uneducated weavers and other manual workers. A number of Catholic priests had become Cathar adherents (Catharism was a religion that seems to have appealed especially to the theologically literate). Worse, the Catholic Church was being held up to public ridicule (some of the richest men in Christendom, bejewelled, vested in finery, and preaching poverty, provided an irresistible target even to contemporary Catholics in the Languedoc). Worst yet, Cathars declined to pay tithes to the Catholic Church. As one senior Churchman observed of the Cathar movement "if it had not been cut back by the swords of the faithful I think it would have corrupted the whole of Europe."

The Cathar view of the Catholic Church was as bleak as the Catholic Church's view of the Cathar Church. On the Cathar side it manifested itself in ridiculing Catholic doctrine and practices, and characterising the Catholic Church as the "Church of Wolves". Catholics accused Cathars of heresy or apostasy and said they belonged to the "Synagogue of Satan". The Catholic side created some striking propaganda. When the propaganda proved unsuccessful, there was only one option left - a crusade - the Albigensian Crusade.

The head of the Catholic Church, Pope Innocent III, called a formal Crusade against the Cathars of the Languedoc, appointing a series of military leaders to head his Holy Army. The first was a Cistercian abbot (Arnaud Amaury), now best remembered for his command at Béziers: "Kill them all. God will know his own". The second was Simon de Montfort now remembered as the father of another Simon de Montfort, a prominent figure in English parliamentary history. The war against the Cathars of the Languedoc continued for two generations. In the later phases the Kings of France would take over as leaders of the crusade, which thus became a Royal Crusade. Among the many victims who lost their lives were two kings: Peter II King of Aragon cut down at the Battle of Muret in 1213 and Louis VIII King of France who succumbed to dysentery on his way home to Paris in 1226.

From 1208, a war of terror was waged against the indigenous population of the Languedoc and their rulers: Raymond VI of Toulouse, Raymond-Roger Trencavel, Raymond Roger of Foix in the first generation and Raymond VII of Toulouse, Raymond Trencavel II, and Roger Bernard II of Foix in the second generation. During this period an estimated half-million Languedoc men, women and children were massacred, Catholics as well as Cathars. The Crusaders killed the locals indiscriminately - in line with the the famous injunction recorded by a Cistercian chronicler as being spoken by his fellow Cistercian, the Abbot in command of the Crusader army at Béziers.

The Counts of Toulouse and their allies were dispossessed and humiliated, and their lands later annexed to France. Educated and tolerant Languedoc rulers were replaced by relative barbarians; Dominic Guzmán (later Saint Dominic) founded the Dominican Order. Within a few years the first papal Inquisition, manned by the Dominicans, was established explicitly to wipe out the last vestiges of resistance.

Persecutions of Languedoc Jews and other minorities were initiated; the culture of the troubadours was lost as their cultured patrons were reduced to wandering refugees known as faidits. Their characteristic concept of "paratge", a whole sophisticated world-view, was almost destroyed, leaving us a pale imitation in our idea of chivalry. Lay learning was discouraged and the reading of the bible became a capital crime. Tithes were enforced. The Languedoc started its long economic decline from the richest region of Europe to become the poorest region in France; and the language of the area, Occitan, began its descent from the foremost literary language in Europe to a regional dialect, disparaged by the French as a patois.

At the end of the extermination of the Cathars, the Roman Church had proof that a sustained campaign of genocide can work. It also had the precedent of an internal Crusade within Christendom, and the machinery of the first modern police state that could be reconstructed for the Spanish Inquisition, and again for later Inquisitions and genocides. Chateaubriand referred to the crusade as "this abominable episode of our history". Voltaire observed that "there was never anything as unjust as the war against the Albigensians".

Catharism is often said to have been completely eradicated soon after the end of the fourteenth century. Yet there are more than a few vestiges even today, apart from the enduring memory of Cathar "Martyrdom" and the ruins of the famous "Cathar castles", including the spectacular castle at Carcassonne and the hilltop Château of Montségur ( Montsegùr).

Today, there are still many echoes of influences from the Cathar period, from International geopolitics down to popular culture. There are even Cathars alive today, or at least people claiming to be modern Cathars. There are historical tours of Cathar sites and also a flourishing, if largely superficial, Cathar tourist industry in the Languedoc, and especially in the Aude département.

As we see the eight-hundredth anniversary of important events, more and more memorials are springing up on the sites of massacres, as at Les Casses, Lavaur, Minerve, and Montségur. There is also an increasing community of historians and other academics engaged in serious historical and other academic Cathar studies. Interestingly, to date, the deeper scholars have dug, the more they have vindicated Cathar claims to represent a survival of an important Gnostic strand of the Earliest Christian Church.

Arguably just as interesting, Protestant ideas share much in common with Cathar ideas, and there is some reason to believe that early reformers were aware of the Cathar tradition. Even today some Protestant Churches claim a Cathar heritage. Tantalisingly, weavers were commonly accused of spreading Protestant ideas in the fifteenth and sixteenth centuries, just as their antecedents in the same trade had been accused of spreading Cathar ideas in Medieval times.

It can even be argued that in many respects Roman Catholic ideas have shifted over the centuries ever further from the Church's medieval teaching and ever closer to Cathar teaching.