From www.metmuseum.org:
Definition of Iconoclasm
Iconoclasm, literally "icon-destruction," was a theological debate involving both the Byzantine church and state. The controversy spanned roughly a century, during the years 726–87 and 815–43. In these decades, imperial legislation barred the production and use of figural images; simultaneously, the cross was promoted as the most acceptable decorative form for Byzantine churches. Archaeological evidence suggests that in certain regions of Byzantium, including Constantinople and Nicaea, existing icons were destroyed or plastered over. Very few early Byzantine icons survived the Iconoclastic period; notable exceptions are woven icons, painted icons preserved at the Monastery of Saint Catherine on Mount Sinai, Egypt, and the miniature icons found on Byzantine coins, including those of Justinian II (r. 685–95; 705–11).
Iconoclasm: The Source of Debate
The Iconoclastic debate centered on the appropriate use of icons in religious veneration, and the precise relationship between the sacred personage and his/her image. Fear that the viewer misdirected his/her veneration toward the image rather than to the holy person represented in the image lay at the heart of this controversy. Old Testament prohibitions against worshipping graven images (Exodus 20:4) provided one of the most important precedents for Byzantine Iconoclasm. The immediate causes for this crisis have been hotly contested by scholars. Among the many suggested causes are the rise of Islam and the emperor's desire to usurp religious authority and funds.
Whats interesting and really sad is how this playing out in mecca. Now the Saudis as we know are guardians of the Holy sites there. But the wing of Islam there is so Iconclast there destroying major historical buildings and artifacts relating to the prophet himself. Thats the reason you see so many modern buildings around there. The view point is tear it down it promotes idolatry. This of course coincides nicely with the fact that new building are reconstructed using Royal Family Construction companies