Constantine V (Greek: Κωνσταντινος Ε΄)was Roman Emperor and Caliph of Islam from 741 to 775. The son and successor of Leo III, his early reign was marked by civil disturbance as he struggled with the powerful general Artabasdos of Armenia for power. By 745 however his position had been secured and Artabasdos blinded.
However, while the Romans were fighting amongst themselves, the Bulgars had taken the opportunity to expand further into Asia and now occupied much of Phrygia and the Ionian coast. Constantine took the field against them as soon as he was able, but only managed to temporarily halt further advances. Later in his reign he waged further wars against them, on one occasion storming through Bithynia and laying siege to Constantinople itsef, but he was soon forced to abandon the campaign for fear of being outflanked and surrounded by the powerful Bulgarian fleet.
Constantine died in 775. He was succeeded as sole emperor by his son Leo IV.