Broadly speaking, the period stretching from 565 (death of Justinian) to 843 (conclusive settlement of the icononoclastic controversy) was a time of troubles in the Byzantine Empire. Major territorial subtractions occurred: Italy (lost to the Lombards), the central-southern Balkans (occupied by the pagan Slavs), and Syria and Egypt (Muslim).
In addition, the Persians invaded, only being defeated with great effort by Heraclius in 628.
Two contrasting examples of art in the time of Heraclius were examined: the Cyprus Plate in the Met of David Fighting Goliath (intensely classicizing) and the mosaic of St. Demetrios (frontal and "Middle Eastern"). This contrast shows that the dichotomy of style, while it was minimized in the time of Justinian, persisted all the same. The classicizing current was to recur throughout later Byzantium, as seen in the Paris Psalter (also showing, inter alii, David).
The early sixth century witnessed a chill in the status of images. The first response, the Jewish one, was the mildest: they simply stopped making images in synagogues. The Muslims had always disapproved of images in mosques. In 721 the Caliph Yazid issued an edict commanding the destruction of such images in Christian churches. Laxly enforced, this step nonetheless was a major step.
In 726, apparently, Leo the Isaurian took the first step of iconoclasm, by destroying a favorite image over the great gate of the Palace in Constantinople. His son Constantine V was especially rigorous. Neither was against images as such, since secular ones appeared, but against religious images, held to be an invitation to idolatry.
The dispute was not finally settled until 843. The iconodules had won--but at a price. No religious figures in the round were allowed. Reverence for icons was supposed to be directed solely at the prototype (the holy figure)--not at the material object.
Beginning apparently in 867, Hagia Sophia was reequipped with images, some of which were seen in class. The Catholicon at Hosios Lukas, a cross-in-square church, demonstrates the hierarchical principle of allocation of mosaics, with Christ in the dome, the Virgin in the main apse, and the other scenes and figures distributed according to rank.