Following a series of heavy military reverses against the Muslims, Iconoclasm emerged within the provinces of the Byzantine Empire in the early 8th century. The First Iconoclasm, as it is sometimes called, occurred between about 726 and 787, while the Second Iconoclasm occurred between 814 and 842. According to the traditional view, Byzantine Iconoclasm was started by a ban on religious images promulgated by the Byzantine Emperor Leo III the Isaurian, and continued under his successors. It was accompanied by widespread destruction of religious images and persecution of supporters of the veneration of images. The iconoclastic movement destroyed much of the Christian Church's early artistic history.

The Papacy remained firmly in support of the use of religious images throughout the period, and the whole episode widened the growing divergence between the Byzantine and Carolingian traditions in what was still a unified European Church, as well as facilitating the reduction or removal of Byzantine political control over parts of the Italian Peninsula. In the Latin West, Pope Gregory III held two synods at Rome and condemned Leo's actions. The Byzantine Iconoclast Council, held at Hieria in 754 CE, ruled that holy portraits were heretical. The iconoclastic movement was later defined as heretical in 787 CE under the Second Council of Nicaea (the seventh ecumenical council) but had a brief resurgence between 815 and 842 CE.