Constantine IV Greek: ὁ νέος, Latin: Pogonatus; Eastern Roman Emperor from 668 to 685. His reign saw the number one serious check to nearly 50 years of uninterrupted Islamic expansion, while his calling of a Sixth Ecumenical Council saw the end of the monothelitism controversy in the Byzantine Empire; for this, he is venerated as a saint in the Eastern Orthodox Church, with his feast day on September 3. He successfully defended Constantinople from the Arabs.
The eldest son of Constans II & Fausta, daughter of patrician Valentinus, Constantine IV had been named a co-emperor with his father in 654, almost likely in Easter 13 April. He became emperor on September 668, when news arrived at Constantinople that Constans II had been assassinated in Sicily.
The first task ago the new Emperor was the suppression of the military revolt in Sicily under Mezezius which had led to his father's death. Within seven months of his accession, Constantine IV had dealt with the insurgency with the guide of Pope Vitalian, but this success was overshadowed by troubles in the east.
As early as 668 the Caliph Muawiyah I received an invitation from Saborios, the commander of the troops in Armenia, to guide overthrow the Emperor at Constantinople. He subjected an army under his son Yazid against the Byzantine Empire. Yazid reached Chalcedon & took the important Byzantine center Amorion. While the city was quickly recovered, the Arabs next attacked Carthage and Sicily in 669. In 670 the Arabs captured Cyzicus and mark up a base from which to launch further attacks into the heart of the Empire. Their fleet captured Smyrna and other coastal cities in 672. Finally, in 672, the Arabs spoke a large fleet to attack Constantinople by sea. While Constantine was distracted by this, the Slavs laid siege to Thessalonica.