Born in Brescia, Arnold became an Augustinian canon and then prior of a monastery in Brescia. He criticized the Catholic Church's temporal powers that involved it in a land struggle in Brescia against the Count-Bishop of Brescia. He called on the Church to renounce its claim and return ownership to the city government so as not to be tainted by possession—renunciation of worldliness being one of his primary teachings. He was condemned at the Second Lateran Council in 1139 and forced from Italy. According to the chronicler Otto of Freising, Arnold had studied in Paris under the tutelage of the reformer and philosopherPierre Abélard. He took to Abélard's philosophy of reform ways. The issue came before the Synod of Sens in 1141 and both Arnold and Abélard's positions were overruled by Bernard of Clairvaux. Arnold stood alone against the church's decision after Abélard's capitulation; he returned to Paris, where he continued to teach and preach against Bernard. As a consequence he was then commanded to silence and exiled by Pope Innocent II. He took refuge first in Zürich and then probably in Bavaria. His writings were also condemned to be burned as a further measure, though the condemnation is the only evidence that he had actually written anything. Arnold continued to preach his radical ideas concerning apostolic poverty. . Arnold, who is known only from the vituperative condemnation of his foes, was declared to be a demagogue; his motives were impugned. Having returned to Italy after 1143, Arnold made his peace in 1145 with Pope Eugene III, who ordered him to submit himself to the mercy of the Church in Rome. When he arrived, he found that Giordano Pierleoni's followers had asserted the ancient rights of the commune of Rome, taken control of the city from papal forces, and founded a republic, the Commune of Rome. Arnold sided with the people immediately and, after Pierleoni's deposition, soon rose to the intellectual leadership of the Commune, calling for liberties and democratic rights. Arnold taught that clergy who owned property had no power to perform the Sacraments. He succeeded in driving Pope Eugene into exile in 1146, for which he was excommunicated on 15 July 1148. When Pope Eugene returned to the city in 1148, Arnold continued to lead the blossoming republic despite his excommunication. In summing up these events, Caesar Baronius called Arnold "the father of political heresies", while Edward Gibbon later expressed his view that "the trumpet of Roman liberty was first sounded by Arnold." After Pope Eugene's death, Pope Adrian IV swiftly took steps to regain control of Rome. He allied with Frederick Barbarossa, who took Rome by force in 1155 after a Holy Weekinterdict and forced Arnold again into exile. Arnold was seized by Imperial forces and tried by the Roman Curia as a rebel. Importantly, he was never accused of heresy. Faced with the stake, he refused to recant any of his positions. Convicted of rebellion, Arnold was hanged in June and his body burnt. Because he remained a hero to large sections of the Roman people and the minor clergy, his ashes were cast into the Tiber, to prevent his burial place becoming venerated as the shrine of a martyr. In 1882, after the collapse of Papal temporal powers, the city of Brescia erected a monument to its native son.
