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Byzantine Iconoclasm occurred during the periods 726-787 AD and 814-842 AD. During these times, many icons were destroyed in the Byzantine empire.
The Byzantine Iconoclasm (Greek: Εικονομαχία, romanized: Eikonomachía, lit. ’image struggle’, ‘war on icons’) were two periods in the history of the Byzantine Empire when the use of religious images or icons was opposed by religious and imperial authorities within the Christian Church (At the time still comprising the Roman-Latin and the Eastern-Orthodox traditions) and the temporal imperial hierarchy. The First Iconoclasm, as it is sometimes called, occurred between about 726 and 787, while the Second Iconoclasm occurred between 814 and 842.
The Byzatines actually called it iconomachy, but modern historians call it iconoclasm.
Iconoclasm is the deliberate destruction within a culture of the culture’s own religious images and other symbols or monuments, usually for religious or political motives. People who engage in or support iconoclasm are called iconoclasts, Greek for “breakers of icons” (εἰκονοκλάσται), a term that has come to be applied figuratively to any person who breaks or disdains established dogmata or conventions. Conversely, people who revere or venerate religious images are derisively called “iconolaters” (εἰκονολάτρες). They are normally known as “iconodules” (εἰκονόδουλοι), or “iconophiles” (εἰκονόφιλοι). These terms were, however, not a part of the Byzantine debate over images. They have been brought into common usage by modern historians (from the seventeenth century) and their application to Byzantium increased considerably in the late twentieth century. The Byzantine term for the debate over religious imagery, “iconomachy,” means “struggle over images” or “image struggle”.
Interestingly, during these periods of iconoclasym, the image of Edessa would not have been affected because Edessa was occupied by the Muslims, starting in the 7th century.
The Armenian chronicler Sebeos, bishop of Bagratid Armenia writing in the 660s, gives the earliest narrative accounts of Islam in any language today. Sebeos writes of a Jewish delegation going to an Arab city (possibly Medina) after the Byzantines conquered Edessa
And it was in 944, after the Byzantine Iconoclasm, that the Edessa image was retaken by the Byantine empire.
Rebuilt by Emperor Justin, and called after him Justinopolis (Evagrius, Hist. Eccl., IV, viii), Edessa was taken in 609 by the Persians, soon retaken by Heraclius, but captured again by the Arabs in 640.
The Byzantines often tried to retake Edessa, especially under Romanus Lacapenus, who obtained from the inhabitants the “Holy Mandylion”, or ancient portrait of Christ, and solemnly transferred it to Constantinople, 16 August, 944.
It was as if the cloth had a mind of its own and knew it would not be safe, even among Christians, and avoided being possibly destroyed by being in “enemy” hands.
Pilgrims had freely travelled to Edessa for many years, even while it was under various empires. It was in the 12th century that tensions arose when it was conquered by Zengi in 1144. This prompted the Second Crusade in 1145-1149.
In 1144, Zengi began the siege of Edessa against the crusader County of Edessa, the weakest and least Latinized crusader state, and captured it on December 24, 1144, after a siege of four months. This event led to the Second Crusade, and later Muslim chroniclers noted it as the start of the jihad against the Crusader states.
The news of the fall of Edessa was brought back to Europe first by pilgrims early in 1145, and then by embassies from Antioch, Jerusalem and Armenia. Bishop Hugh of Jabala reported the news to Pope Eugene III, who issued the bull Quantum praedecessores on 1 December of that year, calling for a second crusade.