The siege of Montsgur was a nine-month siege of the Cathar-held Chteau de Montsgur by French royal forces starting in May 1243. After the castle surrendered, about 210 perfecti and unrepentant credentes were burned in a bonfire on 16 March 1244.



Catharism (; from the Greek: καθαροί, katharoi, "the pure [ones]") was a Christian dualist or Gnostic movement between the 12th and 14th centuries which thrived in Southern Europe, particularly in northern Italy and southern France. Followers were described as Cathars and referred to themselves as Good Christians, and are now mainly remembered for a prolonged period of religious persecution by the Catholic Church, which did not recognize their unorthodox Christianity. Catharism arrived in Western Europe in the Languedoc region of France in the 11th century. The adherents were sometimes referred to as Albigensians, after the city Albi in southern France where the movement first took hold. The belief may have originated in the Byzantine Empire. Catharism was initially taught by ascetic leaders who set few guidelines and so some Catharist practices and beliefs varied by region and over time. The Catholic Church denounced its practices, including the consolamentum ritual by which Cathar individuals were baptised and raised to the status of "Perfect".Catharism was greatly influenced by the Bogomils of the First Bulgarian Empire, and may have also had roots in the Paulician movement in Armenia and eastern Byzantine Anatolia through Paulicians resettled in Thrace (Philipoupolis). Though the term Cathar () has been used for centuries to identify the movement, whether it identified itself with the name is debated. In Cathar texts, the terms Good Men (Bons Hommes), Good Women (Bonnes Femmes), or Good Christians (Bons Chrétiens) are the common terms of self-identification.The idea of two gods or deistic principles, one good and the other evil, was a point of criticism asserted by the Catholic Church against Cathar beliefs. The Catholic Church asserted this was antithetical to monotheism, a fundamental principle that there is only one God, who created all things visible and invisible. Cathars believed that the good God was the God of the New Testament, creator of the spiritual realm, whereas the evil God was the God of the Old Testament, creator of the physical world whom many Cathars identified as Satan. Cathars believed human spirits were the sexless spirits of angels trapped in the material realm of the evil god, destined to be reincarnated until they achieved salvation through the consolamentum, a form of baptism performed when death is imminent, when they would return to the good God.From the beginning of his reign, Pope Innocent III attempted to end Catharism by sending missionaries and by persuading the local authorities to act against them. In 1208, Pierre de Castelnau, Innocent's papal legate, was murdered while returning to Rome after excommunicating Count Raymond VI of Toulouse, who, in his view, was too lenient with the Cathars. Pope Innocent III then abandoned the option of sending Catholic missionaries and jurists, declared Pierre de Castelnau a martyr and launched the Albigensian Crusade in 1209. The Crusade ended in 1229 with the defeat of the Cathars. Catharism underwent persecution by the Medieval Inquisition, which succeeded in eradicating it by 1350.

There is academic controversy about whether Catharism was an organized movement or rather a construct of the medieval Church, which alleged the existence of a heretical group. The lack of any central organization among Cathars, regional differences in beliefs and practices as well as the lack of sources from the Cathars themselves has prompted some scholars to question whether Catharism existed. Other scholars say that there is evidence of the existence of Catharism, and also evidence that the threat of it was exaggerated by its persecutors in the Church.