The people for whose persecution it was designed, and at whose expense it carried on its work, broke into rebellion; the first years of its annals were rendered illustrious by the murder of one of its founders, Pierre de Castelnau.
He was canonized, and became the first Saint of the Inquisition.

Two other Peters obtained the like honor through their zeal for the Catholic faith: Peter of Verona, commonly called Peter Martyr, the Italian saint of the Dominican order; and Peter Arbues, the Spanish saint, who sealed with his blood the charter of the Holy Office in Aragon.
In spite of opposition, the Papal institution took root and flourished.
Philip Augustus responded to the appeals of Innocent; and a crusade began against the Albigenses, in which Simon de Montfort won his sinister celebrity.

During those bloody wars the Inquisition developed itself as a force of formidable expansive energy.

Material assistance to the cause was rendered by a Spanish monk of the Augustine order, who settled in Provence on his way back from Rome in 1206.

Domenigo de Guzman, known to universal history as S.Dominic, organized a new militia for the service of the orthodox Church between the years 1215 and 1219.