Author guest post from Leslie Ivings.

Constantine V has long been remembered as Byzantium’s most notorious iconoclast, mocked by his enemies as a tyrant and persecutor. Yet behind the hostile accounts lies a very different story: that of a soldier-emperor who forged one of the most formidable armies of the Middle Ages. By reshaping the empire’s military system, leading campaigns in person, and securing vital victories against the Bulgars, Constantine ensured the survival of Byzantium for generations. This article re-examines the emperor everyone loved to hate as the architect of a military machine.

When Constantine V came to the throne in 741, the Byzantine Empire was still staggering from a century of crisis. Arab armies had swept across the Near East, the Balkans were restless and dangerous, and the internal wounds of civil war had scarcely healed. It was not obvious that Byzantium would survive into the ninth century, let alone enter what some historians now call its “second golden age.” And yet it did survive, and much of the credit belongs to Constantine V, an emperor remembered in the hostile chronicles as a cruel persecutor, but who in practice forged one of the most formidable military machines of the early Middle Ages.

Constantine’s achievements in this sphere are easily overlooked, buried beneath the legend of Kopronymos, the “dung-named” tyrant mocked by monastic chroniclers. But behind the polemic lies a general of rare energy and organisational talent, whose reforms gave Byzantium the resilience to resist its enemies for generations. To understand his reign, one must set aside the venom of his critics and look instead at the cold logic of strategy, administration, and the battlefield.

Unlike some emperors who ruled largely from the palace, Constantine V was happiest in the saddle. His reign was punctuated by long campaigning seasons, especially against the Bulgars in the Balkans. These campaigns were not always decisive, for border wars rarely are, but they established a rhythm of constant pressure, keeping enemies off balance and projecting imperial power far beyond the walls of Constantinople.

Chroniclers admit, despite themselves, that Constantine was a tireless commander. He reorganised the army on thematic lines, refining a system that had begun to take shape under his father Leo III. The themes, regional districts that supplied troops and provisions, became the backbone of imperial defence. Soldiers were settled on military lands, ensuring a pool of manpower that was both loyal and self-sustaining. This was not the Roman legionary system of old, but it was ideally suited to an empire under siege, offering flexibility, rapid mobilisation, and resilience.

Constantine personally led many expeditions north of the Haemus Mountains. The Bulgars were fierce opponents, skilled in ambush and mobile cavalry tactics, but Constantine’s relentless campaigning gradually shifted the balance of power. Even hostile sources concede his successes: fortresses were taken, territories resettled, and tribute imposed. For all the caricatures of cruelty, there was also a shrewd strategic mind at work.

Constantine understood that armies win wars not just through courage but through structure. He sought to bind the army to the state more tightly than ever before. The thematic system was refined with careful attention to recruitment and land grants. Officers were appointed with loyalty as well as competence in mind, ensuring that the army remained a pillar of his throne.

Equally important was supply. A campaigning army lives or dies by its logistics, and Constantine invested heavily in the infrastructure to support prolonged operations. The empire’s fiscal machinery, tightened by reforms to taxation and resettlement, ensured that soldiers were provisioned and paid. The Byzantine state under Constantine looked, in some ways, like a vast war economy, oriented towards the survival of the capital and the projection of power at its borders.

Naval forces, too, were not neglected. The empire’s survival had always depended on the sea, and Constantine maintained and strengthened the fleet, inheriting his father’s secret weapon of Greek fire. This ensured that Constantinople, impregnable behind its walls and defended by fire-belching ships, could not be taken by siege. The mere existence of such a navy was a deterrent, projecting Byzantine authority across the Aegean and keeping Arab raiders in check.

It must be admitted that Constantine’s army machine was built not only on efficiency but also on fear. His critics dwell gleefully on punishments, executions, and brutal reprisals against those who opposed him. Yet here, too, we see the logic of a general who valued discipline above all else. An army that mutinies is worse than useless, and the empire could not afford disunity.

One infamous episode occurred in 766, when a conspiracy against the emperor was uncovered among high-ranking officers. The punishment was public, spectacular, and merciless, a reminder to all that disloyalty would not be tolerated. To modern eyes, it appears savage. To Constantine, it was the only way to preserve the integrity of a system upon which the survival of the empire depended.

Even the resettlement policies for which he is condemned, deporting populations to reinforce strategic zones, can be read through this lens. They strengthened border regions, populated depopulated areas, and ensured that the army’s manpower pool was constantly replenished. Cruel, yes; effective, certainly.

The pinnacle of Constantine’s military career came in 763 at the Battle of Anchialus, one of the great set-piece clashes of the eighth century. With some 50,000 men, Constantine met the Bulgars in a pitched engagement near the Black Sea. The chroniclers, loath to give him credit, nevertheless admit to a stunning victory, with Bulgar casualties so heavy that their khan barely escaped with his life.

Anchialus was not the end of the Bulgar problem, but it secured Constantinople’s northern frontier for a generation. More than that, it symbolised the new strength of the Byzantine army, disciplined, organised, and capable of decisive battlefield success. The emperor returned to the capital in triumph, and for his supporters at least, Constantine V was a second Justinian, a restorer of imperial glory.

Why, then, is this military emperor remembered as a monster rather than a saviour? The answer lies in the politics of religion. Constantine’s iconoclasm, his rejection of religious images, brought him into direct conflict with powerful monastic institutions. It is they who preserved the written record, and it is through their eyes that later generations have seen him. To them, Constantine was not a general or reformer but the Antichrist himself.

The irony is striking: the emperor who secured the empire’s borders, rebuilt its capital, and reformed its army was remembered not for saving Byzantium but for persecuting icons. His military machine, so vital to the empire’s survival, was almost erased from the narrative. Yet without it, there could have been no revival under later emperors, no flourishing of Byzantine culture, no empire at all for the chroniclers to serve.

Constantine V deserves to be seen, at the very least, as a paradox: a ruler whose military genius was hidden beneath a cloak of infamy. His reforms shaped the army that would defend Byzantium for centuries. His victories checked the Bulgars, contained the Arabs, and ensured the survival of Constantinople. His machine was not pretty, and it was built on coercion as well as skill, but it worked.

In the end, Constantine’s story is a reminder of how fragile reputation can be. A man who saved an empire was remembered as a tyrant because his policies offended the guardians of memory. To modern historians, and to general readers, he offers a fascinating case study in how power, religion, and propaganda intertwine.

As the empire’s enemies closed in, Constantine V did not retreat into the palace or cloister. He mounted his horse, took command of his troops, and marched to the frontier. Few emperors did more to ensure Byzantium’s survival, and few have been so unfairly maligned.

To explore Constantine V’s reign in full, from his military triumphs to the bitter controversies that shaped his legacy, see my new book Byzantine Emperor Constantine V: The Dung-named, available now from Pen & Sword.