BY 1200 Catharism was firmly established in many parts of western Europe, particularly in Languedoc, Catalonia, Lombardy and Tuscany. There were several thousand perfected Cathars, which implies that there must have been tens of thousands of people with Cathar sympathies. Statistically they were insignificant even in areas where their support was strongest, but they could not be disregarded by the Catholic authorities because they had an excellent organisation and a coherent system of belief. Wherever their numbers warranted it, they set up territorial bishoprics, subdivided into deaconries, and organised the perfecti in single-sex communities with a variety of pastoral or contemplative functions. They taught that the Catholic Church had been founded by the powers of evil, and that its sacraments could not confer salvation; and this made any kind of compromise impossible.

Innocent III considered them an international threat. In the first year of his reign Cathar supporters were accused of assassinating his podestà of Orvieto in the Papal States, and the pope was informed that the ruler of Christian Bosnia, with many of his subjects, had professed the dualist faith. Although in 1203 Bosnia returned to the Roman obedience in response to Hungarian pressure, Innocent became aware of the true extent of Balkan dualism in 1204 when the Bulgarian Church acknowledged the papal primacy, and the Fourth Crusade set up a Latin patriarch in Constantinople. He may have instigated the repressive measures against Balkan dualism in the Synodikon of Tsar Boril (1211). In the western Church he directed his attention chiefly to the suppression of Catharism in Languedoc.