Thus the Dominicans, and to a lesser extent the Franciscans, were sent to the places where heresy most abounded. Some went to Germany, but no formal and permanent Tribunal was established there until 1367. Alberic, a Dominican, was sent to Lombardy, with the title, “Inquisitor hereticae pravitatis”. One of his successors was killed by a mob; another, Saint Peter of Verona, Dominican son of Manichee parents and founder of the Inquisition at Florence about 1245, was assassinated by heretics on the road from Como to Milan in 1252. It was dangerous business, being an Inquisitor, for the heretics were often rich and influential, with the courage of fanaticism and despair. Hunting them out was not a task that any young Dominican aspired to for its own sake. This was particularly true in southern France, where the Cathari, having survived the Crusade, put up a long and stubborn fight against the new monastic courts. A Dominican convent was sacked by some heretics in 1234. Eight years later the Inquisitor Arnaud and several other Dominicans were assassinated. The Dominicans then asked the Pope (Innocent IV) to relieve them of the mission. This he refused to do. In 1244 an armed force of Catholics broke the resistance of the Cathari by storming Montsegur, whence the murderers of the Dominicans had ridden forth, and burned 200 heretics without trial, even as the Levites of Moses had slain the idolaters. After that the Inquisition was accepted by the secular officials. Gregory IX sent Inquisitors to Spain in 1238. One of them was poisoned by heretics.
In his instructions to his emissaries, the Pope created the form which distinguished the Medieval Inquisitions from the bishops’ investigations and all other previous Christian attempts to deal with the problem of heresy. Into a town, reported to be infected with heresy, the friars were to go and publicly proclaim that all guilty of offenses against the Faith must appear and abjure their errors. Those who did so were to be forgiven. To detect those who did not, the friars were to set in motion an Inquiry; and if two witnesses testified that such and such a man was a heretic, they must place him on trial, acting at all times, of course, in cooperation with, and only with the consent of, the Bishop. There was no provision for torture; it was not used for about 20 years.
Gregory apparently had no intention of founding a new institution. He was making use of the new religious orders to help the Bishops in a duty that had always been theirs. Bishop Douais, a profound student of source documents of the early Inquisition, believed he was also trying to forestall encroachments by Frederic II, who had already begun to burn political enemies on the pretext that he was defending the Faith. Gregory proposed to decide by theological experts, not by politicians or soldiers, who was a true Catholic and who was not. Once that question was answered, the Church was free to reconcile or excommunicate the guilty, and the State, if it considered him dangerous enough, could inflict on him the usual penalty for high treason.
William Thomas Walsh, Characters of the Inquisition (1940)