(Greek eikon, “image”; klaein, “to break”), any movement against the religious use of images, especially the one that disturbed the Byzantine Empire in the 8th and 9th centuries. In 726 and 730 Emperor Leo III, the Isaurian, promulgated a decree forbidding the veneration of images. This decision was condemned by the pope, but the iconoclastic doctrine was rigorously enforced at Constantinople (present-day stanbul) by Leo and even more by his son and successor Constantine V, who had the worship of images condemned as idolatry at the church council held in the suburban palace of Hieria in 754. The accession of Empress Irene brought with it a change in policy, and the iconoclasts were condemned in turn at the second Council of Nicaea, in 787. A second period of iconoclasm was inaugurated under imperial auspices in the first half of the 9th century; it ended with the final condemnation of iconoclasm at the Council of Orthodoxy, held in 843 under the patronage of Empress Theodora II.
The most serious argument against iconoclasm formulated by the Syrian theologian and Father of the Church John of Damascus was that it denied one of the fundamental tenets of the Christian faith, the doctrine of the incarnation. According to the defenders of images, Christ’s human birth had made possible his representations, which in some sense shared in the divinity of their prototype. The rejection of these images, therefore, automatically carried a repudiation of their cause.
In addition to its theological aspects, the iconoclastic movement seriously affected Byzantine art. Furthermore, the movement weakened the position of the empire by fomenting internal quarrels and splitting with the papacy, which began to abandon its Byzantine allegiance and seek alliance with the Franks. Despite its victory in the theological sphere, the Eastern church was not successful in its challenge of imperial authority, even with John of Damascus’s assertion that the emperor had no right to interfere in matters of faith. Both the introduction of iconoclasm and its condemnation at the councils of 787 and 843 were ultimately the result of imperial rather than ecclesiastical decisions, because the councils met only on imperial orders. Consequently, the authority of the emperor in both the spiritual and the secular spheres, and his control of the church, emerged from the controversy perceptibly strengthened.