In 1184 at Verona in Italy, Pope Lucius III and the Emperor, Frederick Barbarossa, jointly issued an important decree, Ad abolendam, condemning heresy and heretics…Local bishops were instructed to make an official visitation, once or twice a year, of every parish in their diocese where heretics were reputed to live, either personally or through a representative assisted by honest and capable men. In each parish the bishop was required to request three or more trustworthy men to report under oath any heretical activities that had come to their attention…The inquiry completed, the accused were to be cited before the bishop’s tribunal.
From this point on the process is somewhat vague. It was possible that the accused could clear himself by the accepted methods of the customary law. Otherwise the bishop would convene his court. As a judge he took into consideration the gravity of the offense and the circumstances relevant to the person involved. If the heretic was a cleric he might be permitted to purge himself by spontaneously and immediately returning to the unity of the faith by publicly abjuring his errors and by giving guarantees of his sincerity. Otherwise he was to be degraded, deprived of all offices and benefices, and be handed over to the secular arm for due punishment, animadversione debita puniendus. Laymen were able to purge themselves by abjuring heresy, by giving pledges of their sincerity, and by promptly returning to the orthodox faith. Relapsed heretics were to be handed over summarily to the secular arm for due punishment as their first conversion was now regarded as insincere. Due punishment, at this time, meant exile and the confiscation of one’s property. All incurred the canonical and civil stigma of infamy (infamia), a legal term debarring a person from obtaining any ecclesiastical office or dignity, from pleading in court or giving testimony, and from exercising any public office. In their turn the counts, barons, podestas, and consuls of all cities were required to take a special oath to assist faithfully and effectively church authorities against the heretics when called upon. Furthermore by reason of their office they were ordered to execute assiduously the mandates of ecclesiastical and imperial Constitutions.
However detailed this decree may seem to be, it did not represent anything radically new. The local bishop always had had the duty of canonically visiting the parishes of his diocese – as he does today – and of protecting his flock from the ravages of false doctrine. Even the denunciations against heretical suspects do not originate with the bishop himself. Rather they are the result of public scandal, reports, rumors adduced by sworn witnesses. Hence the procedure remained basically accusatory by private citizens.
Albert Shannon, The Medieval Inquisition (1991)