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Constantine IV,c.652–685, Byzantine emperor (668–85), son and successor of Constans IIConstans II
(Constans Pogonatus), 630–68, Byzantine emperor (641–68), son and successor of Constantine III and grandson of Heraclius. Early in his reign Armenia and Asia Minor were invaded by the Muslims, who challenged Byzantine supremacy at sea, took Cyprus, and
..... Click the link for more information. . He defended Constantinople against the annual naval attacks of the Muslims, who finally withdrew in 678; Greek fireGreek fire,
a flammable composition believed to have consisted of sulfur, naphtha, and quicklime. Although known in antiquity, it was first employed on a large scale by the Byzantines.
..... Click the link for more information. was a conspicuous weapon in the defense. Severely defeated (679) by the Bulgars, Constantine ceded them territory S of the Danube, where they founded a kingdom. In 680 he summoned the Third Council of ConstantinopleConstantinople, Third Council of,
680, regarded by Roman Catholic and Orthodox Eastern churches as the sixth ecumenical council. It was convoked by Byzantine Emperor Constantine IV to deal with Monotheletism.
..... Click the link for more information. , which briefly reestablished peace between the Eastern and Western churches by condemning MonotheletismMonotheletism
[Gr.,=one will], 7th-century opinion condemned as heretical by the Third Council of Constantinople in 680 (see Constantinople, Third Council of).
..... Click the link for more information. . Constantine was succeeded by his son, Justinian IIJustinian II
(Justinian Rhinotmetus), 669–711, Byzantine emperor (685–95, 705–11), son and successor of Constantine IV. He successfully invaded Arab territory but lost the advantage through a truce that ceded much of Asia Minor to the Arabs.
..... Click the link for more information. .