The term ‘Medieval Inquisition’ covers series of inquisitions from 1184 to the 1230s.
Pope Lucius III opens the Episcopal Inquisition in 1184 to combat the heretical Cathars and Waldensians. Both groups are excommunicated, and the pope issues a bull to instruct his bishops to comb their jurisdictions for heretics twice every year.
Innocent III steps up the inquisition in 1199 and makes heresy a form of high treason. In 1208, the pope orders a crusade on the Cathars and between 10-15,000 are massacred in the town of Beziers.
In 1231, Pope Gregory IX orders Dominicans in the German city of Regensburg to “seek out diligently those who are heretics or are inflamed of heresy”. An increasing number of people are burned to death in the following decade.