Constantine V (Greek: Κωνσταντῖνος Ε΄; denigrated by his enemies as Kopronymos or Copronymus, meaning the dung-named) was Byzantine Emperor from 741 to 775.
Constantine was an able general and administrator. He reorganised the themes, the military districts of the Empire, and created new field army divisions called tagmata. This organization was intended to minimize the threat of conspiracies and to enhance the defensive capabilities of the Empire. With this reorganized army he embarked on campaigns on the three major frontiers.
In 746, profiting by the unstable conditions in the Umayyad Caliphate, which was falling apart under Marwan II, Constantine invaded Syria and captured Germanikeia (modern Maraş, his father's birthplace). He organised the resettlement of part of the local Christian population to Imperial territory in Thrace. In 747 his fleet destroyed the Arab fleet off Cyprus. In 752 he led an invasion into the new Abbasid Caliphate under As-Saffah. Constantine captured Theodosioupolis and Melitene (Malatya) and again resettled some of the population in the Balkans. These campaigns failed to secure any concrete gains (apart from additional population employed to strengthen another frontier), but it is important to note that under Constantine V the Empire had gone on the offensive.
Meanwhile, with Constantine occupied, Lombard king Aistulf captured Ravenna in 755, ending over two centuries of Byzantine rule.
The successes in the east made it possible to pursue an aggressive policy in the Balkans. With the resettlement of Christian populations from the East into Thrace, Constantine V aimed to enhance the prosperity and defence of the area, causing concern to the Empire's northern neighbour, Bulgaria, and leading the two states to clash in 755. Kormisosh of Bulgaria raided as far as the Anastasian Wall but was defeated in battle by Constantine V, who inaugurated a long series of nine successful campaigns against the Bulgarians in the next year, scoring a victory over Kormisosh's successor Vinekh at Marcelae.
Three years later, Constantine was defeated in the battle of the Rishki Pass, but the Bulgarians did not exploit their success. In 763, he sailed to Anchialus with 800 ships carrying 9,600 cavalry and some infantry. Constantine's victories, including that at Anchialus in 763, caused considerable instability in Bulgaria, where six monarchs lost their crowns on account of their failures.
In 775, Constantine was persuaded to reveal to the Bulgarian ruler Telerig the identities of his agents in Bulgaria, and they were promptly eliminated. Constantine thus began preparations for a new campaign against the Bulgarians, during which he died, on September 14, 775.
Constantine V ruled as sole Emperor until he crowned his son Leo IV ("the Khazar") as co-emperor in 751, when Leo was still an infant.