Icons In the 820s, a controversy emerged over the iconoclastic policies of bishop Claudius of Turin. This stance was opposed by Dungal of Bobbio at the request of Louis the Pious. Agobard, in his Book on Paintings and Images, came out in opposition to Dungal's method of using secular knowledge to justify veneration of images. Political Problems In the 820s, Agobard had already shown his willingness to challenge Louis the Pious on the subject of Jews and on secular holdings of church land. Agobard continued to confront the emperor, particularly on the issues of royal succession and the matter of land ownership. Agobard accused the emperor of abandoning his 817 Ordinatio imperii decree, which promoted an all-encompassing unity of church and empire. In both of the two rebellions against Louis, 830 and 833, Agobard supported the ill-fated revolt of Louis' son Lothair I. In 833, when Lothair launched his second revolt, Agobard published his support for Lothair once more in several works: A Comparison of Ecclesiastical and Political Government and Wherein the Dignity of the Church Outshines the Majesty of Empires and the Liber Apologeticus in defense of the rebelling sons of Louis. Exile and Return After Louis was restored to his power, backed by his sons Louis the German and Pepin I of Aquitaine, Agobard was suspended from his episcopate by the Council of Thionville and exiled, replaced by the chorbishop Amalarius of Metz (). During his tenure in Lyon, Amalarius worked to impose liturgical reforms upon the archdiocese of Lyon. Amalarius' reforms were characterized by a heavy reliance upon allegorical and symbolic representations within the Mass. Agobard, on the other hand, disdained Amalarius' reforms as "theatrical" and "showy" and favored a more plain liturgy. Amalarius' reforms were also opposed by Agobard's disciple Florus of Lyon; Amalarius was deposed and accused of heresy in 838. Agobard wrote three works against Amalarius: On Divine Psalmody, On the Correction of the Antiphonary, and Liber officialis. When he returned to Lyon, Agobard worked to roll back Amalarius' actions, with the support of Florus. Other works During his life, Agobard wrote more works on other issues, including several against pagan practices, two on the role of clergy, and a treatise on icons. Agobard also wrote a treatise arguing against weather magic called De Grandine et Tonitruis ("On Hail and Thunder"). A passage in it mentions the popular belief in ships in the clouds