Pope Lucius III in the context of "Frederick I, Holy Roman Emperor"

Pope Gregory IX (Latin: Gregorius IX; born Ugolino di Conti; 1145 – 22 August 1241) was head of the Catholic Church and the ruler of the Papal States from 19 March 1227 until his death in 1241. He is known for issuing the Decretales and instituting the Papal Inquisition, in response to the failures of the episcopal inquisitions established during the time of Pope Lucius III, by means of the papal bull Ad abolendam, issued in 1184.

He worked initially as a cardinal, and after becoming the successor of Honorius III, he fully inherited the traditions of Gregory VII and of his own cousin Innocent III, and zealously continued their policy of papal supremacy.

Ad abolendam (lit. 'On abolition / Towards abolishing'; full title in Latin: Ad abolendam diversam haeresium pravitatem, lit. 'To abolish diverse malignant heresies') was a decretal and bull of Pope Lucius III, written at Verona and issued 4 November 1184. It was issued after the Council of Verona settled some jurisdictional differences between the Papacy and Frederick I, Holy Roman Emperor. The document prescribes measures to uproot heresy and sparked the efforts which culminated in the Albigensian Crusade and the Inquisitions. Its chief aim was the complete abolition of Christian heresy.

The Synod of Verona was held November 1184 under the auspices of Pope Lucius III and the Holy Roman Emperor Frederick I.

The meeting was to address numerous issues. Some of these were the dispute over claims between empire and papacy in central Italy, the proprietary concerns of the bishopric of Gurk, plans for a crusade to the Holy Land, a dispute over the investiture of the rival Archbishops of Trier, Folmar of Karden (the pro-papal candidate) and Rudolf of Wied (afterward invested as anti-archbishop by Barbarossa under the terms of the Concordat of Worms), and the condemnation of heresy. It also addressed the issue of marriage, particularly in response to the condemnation of marriage by the Cathars, finally listing it as a sacrament.