Charged them to preach among the Albigensian heretics in Languedoc. For ten years (1205-1215) this mission in Languedoc was the work of Dominic's life.
In 1836 he was elected a member of the Academy of Inscriptions, and in 1837 he published (with an introduction the conclusions of which would not now all be endorsed) a translation of a Provencal poem on the Albigensian war.
Called on the Christian princes to suppress the Albigensian heresy by force of arms, and for seven years the south of France was devastated by one of the most bloodthirsty wars in history, the Albigenses being slaughtered by thousands and their property confiscated wholesale.
The oldest trustworthy sources know nothing of his having exercised the office of Inquisitor during the Albigensian war" (Griitzmacher).
He used often to organize formal disputations with Albigensian leaders, lasting a number of days.