Leo III ruled the eastern empire from 717 to 741, held Constantinople through a twelve-month Umayyad siege in the first year of his reign, and began the iconoclast policy that made his memory a battleground.
Leo III came to the throne in March 717 and spent his first year as emperor under siege. An Umayyad army and fleet arrived in August intending to take the city and end the empire, and twelve months later they were gone, the fleet burned and the army starved.
That single achievement would have secured his reputation. Instead his name is attached to iconoclasm — the removal of religious images from churches and public places — and the writers who preserved the seventh and eighth centuries were the party that eventually defeated it.
The result is an unusually distorted record. The same authors who describe his defence of the city with something close to admiration explain the rest of his reign as the work of a heretic, and there is almost no independent tradition to set against them.
He was born in the 680s at Germanikeia in northern Syria, in territory the caliphate had taken, and his birth name was Konon. His family was resettled in Thrace under Justinian II, which is how a Syrian provincial ended up in imperial service.
The epithet "the Isaurian" attached to him and to his dynasty is probably a mistake. Isauria is in southern Anatolia and he was not from it; the label appears in later sources and has stuck to the dynasty regardless of the geography.
He rose through the reign of Justinian II — a diplomatic mission to the Caucasus, then command of the Anatolic theme, the largest and most exposed of the military provinces. By 716 he was the senior soldier facing the Umayyad advance, and the empire had spent twenty years going through emperors at a rate of one every three or four years.
Reading his character requires allowing for the source problem throughout. Theophanes and Nikephoros wrote after iconoclasm had been defeated and regarded him as the man who began it, so praise from them is more reliable than criticism.
What survives of that praise is consistently practical: a commander who prepared, who used the fleet rather than trusting the walls alone, who kept the city fed, and who was not panicked by a year of blockade. His negotiation with Maslama before the siege — whether it was a deception or an understanding that later broke down — shows a man comfortable operating on both sides of a frontier he had grown up on.
The hostile material describes a hard, obstinate ruler who forced a religious policy on an unwilling church and city. Some of that is likely true and some is the standard vocabulary applied to any emperor the tradition condemned. What cannot be recovered is his own account of why he did it: nothing he wrote about images survives except through the pens of people refuting him.
In 716 the Umayyads advanced through Anatolia under Maslama, and Leo, as strategos of the Anatolics, dealt with him directly. The Byzantine tradition says he strung Maslama along with promises of submission and used the delay to march on the capital; the Arabic tradition says Maslama supported him and was betrayed.
Theodosius III, an unwilling emperor raised by a mutiny of the Opsikian troops, saw what was coming and made terms. He abdicated in March 717 and entered a monastery, and Leo was crowned in Hagia Sophia.
It was a usurpation, the sixth in twenty years, and it was accepted because the alternative was facing the largest invasion in living memory under a man nobody thought capable of it.
The Umayyad army reached the land walls in August 717 and built its own wall facing the city; the fleet came in September to close the Bosphorus and starve it out. Leo's answer was the fleet and the fire.
Byzantine ships attacked the squadrons as they moved into the strait and destroyed much of the fleet with Greek fire, and the sea blockade was never properly re-established. The besiegers spent a brutal winter outside a city that was still being supplied, lost their Egyptian reinforcement squadrons to mass desertion in the spring, and were attacked from the north by the Bulgars.
The siege was lifted on 15 August 718 and the returning fleet was wrecked by storms. Leo had been emperor for seventeen months and had destroyed the offensive capability the caliphate had spent years assembling.
The rest of the reign was reconstruction. He continued the reorganisation of the provinces into themes — military districts under a strategos, which put soldiers on land they had a reason to defend — and split the oversized Anatolic and Opsikian commands that had produced so many usurpers, including himself.
In 726 he issued the Ecloga, a short practical revision of Justinian's law in Greek rather than Latin, aimed at judges who had to use it. It reduced the death penalty in favour of mutilation — which reads as barbarous now and was intended as leniency then — and strengthened protections in marriage and inheritance for wives and children.
He also restored the state's finances and its frontier defence to the point where the Umayyad raids of the 720s and 730s, damaging as they were, no longer threatened the empire's existence. In 740 he and his son beat a major raiding army at Akroinon in Phrygia.