Constantine IV

Constantine IV (c. 650–685) was Byzantine emperor from 668, the eldest son of Constans II. He first crushed the Sicilian usurper Mezezius. Arab fleets assaulted Constantinople from 670, but his defence forced Caliph Mu'awiya I to sue for peace, the first major Arab reverse in fifty years.

In 680 he convened the Sixth Ecumenical Council, which condemned monothelitism. He besieged Khan Asparukh's Bulgars in their fortified camp, but illness forced him to leave the army and it was defeated. In 681 he recognized their state in Moesia and paid them tribute. He died of dysentery in 685 and was succeeded by his son Justinian II.