The Cathar Albigensians were having a rather rough go of it by 1200 AD. Even though the essential foundations of their faith predated the Catholic Church by over a millennium, in the end it was precisely that blend of Manichean philosophy and Christianity which the Mother Church in Rome felt to be truly threatening. From their perspective, after all, the Crusades had been a miserable failure in the end, yet contact between Europe and the Islamic East was more entrenched than ever, socially and economically. Now, suddenly, you had these rural Christians in Catalonia, Lombardy and Tuscany, all whispering the ascetic mysticism of some Syrian prophet, named Mani, who had been dead some thousand years, even when they still had the gall to claim to still be Christians. They retreated from work (often on the farms of Church monasteries, growing food to support the monks and friars) and dared form their own communities; fully initiated members of the Cathar Church (which soon had its own bishops and deacons) referred to themselves as the ’perfecti’. They argued, through the lens of Eastern idealist philosophy (which in turn was a Persian elaboration upon neo-Platonism) that, a) the Holy Roman Catholic Church sold salvation through meaningless, ritualistic sacraments, and b) the Church hierarchy was the work of diabolical forces. It was, in other words, a kind of Lutheranism arrived two centuries early, and needless to say, Pope Innocent III promptly and most righteously freaked.
    How bad did the Pope lose it? Innocent III was the first Church leader in centuries faced with the threat of a popular, grass-roots heresy of the dualist bent – sure, there had been Gnostic schisms at the time of the early Church Fathers but all that nonsense had been dealt with (largely through the detailed elaboration of the Doctrine of Hell and Purgatory, as well as an elaborate iconographic architecture devoted to the aesthetic resolution of the glaring contradiction inherent in the Holy Trinity).
    In any case, the stakes were high as dualism began to seep again through the communities of Christendom, from the villas of Champagne to the hovels of Bosnia. Actually, especially in Bosnia as it turns out, where many of the Christians were in close contact with the Eastern mythic element of Asia Minor. The Balkans were particularly open to the thought of the East.
    By 1206, Innocent III was convinced there was a dire threat in these Eastern influences; Sicily, Malta, most of Spain had all been under the sway of the infidel (in one form or another) for centuries at a time; only with the Crusades had these lands been re-secured, even if the ultimate goal of the Holy Sepulcher had slipped again from Western hands. The real importance, now that the holy wars were over abroad, was no to start losing them at home as well. Heresy, then, was seen in military terms – a matter of spiritual as well as national security – and in 1206, the pope dispatched his best agents, the ‘legates’, who acted essentially under-cover. They fanned out along the roadways of Spain, France, Germany and into the Balkans – dressed in drab, friars clothes, they begged, slept in fields, and still preached but spoke nothing of Rome or their real mission.
    By 1208, however, the presence of a special papal Agent, Peter of Castelnaw, circulating in the region of Toulouse infuriated the local duke Raymond VI, and when the holy ‘legate’ was found missing his eyes, Innocent III realized Cathar or not, that region of France was going to be trouble. Raymond of Toulouse was promptly branded a Cathar by the Church, and a very special, forty-day, one-time-only Crusade was declared against the region in reprisal and to make an example of Raymond VI before the pope was seen in Rome as being ‘weak on the heretics’ (likely the 13th c. version of ‘slave to the special-interest vote’). Besides, it got the ruffians working, gave them sometime to do.
    Anyway, into the Albi and Toulouse regions of France did soon pour all the puffed-up unemployed mercenaries and farm-hands of Europe, burning fields, pillaging homesteads, stealing the sheep, drinking the wine, and likely much worse along the way, for a very clearly marked-out forty days of Particularly Prescribed Papal Punishment. This was a great deal for the Crusaders – after all, no one had taken up the Cross in ages, and certainly never with such a conveniently placed target – ‘…you know Albi, right there, middle of Europe, close to all amenities and all mod cons. None of this, ‘Off to the Holy Land’ bother…’ – and the spiritual indulgences offered were the same as ‘real’ Crusaders. By June of 1209, the knight Arnald-Amalric led the mustered troops down the Rhone toward the town of Toulouse itself.
    When Raymond heard the holy appointed ne’er-do-well’s off southern Europe were en route with holy orders to wreak havoc on his town, he needless to say grabbed as many Church officials as he could find at the last minute and said many apologies – he offered land, he signed over deeds to castles, he wrote apologetic treatises in tears and blood, he had himself publicly flogged while begging the forgiveness of Pope Innocent, the Lord-Blessed Mary, and the Father, Son and the Holy Ghost – in that order – but none of it worked. For, as we all know, once you're the Pope (or any theocrat for that matter) and you kick off a most-righteously holy war, these things have tend to develop their own momentum. When the town of Belziers fell July 22, 1209, every Christian man, woman and child were tied with stones and drowned, in order to bring the entire region quickly into submission, and when the siege of Lavaur ended long after, the 400 Cathar ‘perfecti’ found in hiding their were burned alive in the catacombs where they hid.
Source: Bernard Hamilton, “The Albigensian Crusade and Heresy”, fr. The New Cambridge Medieval History, v. 5 (1999), pp. 164 – 168.