On 3 September 863 a Byzantine army under Petronas encircled and destroyed the raiding army of Umar al-Aqta, emir of Melitene, at the river Lalakaon. The emir was killed and the eastern frontier never looked the same.
In the summer of 863 Umar al-Aqta, emir of Melitene, led a raiding army across Anatolia to Amisos on the Black Sea. It was the kind of expedition he had been making for three decades, and the kind Byzantine emperors had been enduring for two centuries.
On the way back he was intercepted. Petronas, uncle of the emperor Michael III, brought three armies together from the west, the east and the north, closed them around the raiders in the valley of the Lalakaon, and destroyed the force on 3 September. The emir was killed.
Everything about the eastern frontier changed afterwards. The emirate of Melitene, which had been the most dangerous raiding power on the border, was finished as an offensive threat, and within seventy years Byzantine armies were taking the frontier cities themselves.
The Arab–Byzantine frontier was not a line but a zone — the Thughur, a belt of fortified cities on the Arab side facing the Byzantine themes across the Taurus and Anti-Taurus. Its emirs raided under their own authority, and the most effective of them held Melitene on the upper Euphrates.
Umar al-Aqta had held it since the 830s and had made himself the terror of Anatolia, often campaigning in concert with the Paulicians of Tephrike, a heretical Christian community that had made common cause with the emirate against the empire.
What had changed by 863 was not on the frontier but behind it. The Abbasid caliphate had fallen into the crisis known as the anarchy at Samarra: caliphs raised and murdered by their own Turkish troops, and no central authority able to support or restrain the frontier emirs. Melitene raided in 863 with nothing behind it.
Petronas commanded the response, holding the office of Domestic of the Schools, and the plan was an encirclement rather than an interception: forces from the western themes, from the eastern themes and from the Black Sea coast converged on the returning raiders.
The armies met at the Lalakaon, in Paphlagonia, on 3 September 863. The Byzantines closed the ring and held the high ground, and the raiders were caught in a valley with no line of retreat that had not already been blocked.
Umar al-Aqta was killed trying to break out. His army was destroyed almost entirely, and a second column under the emir of Tarsus was intercepted and beaten in the same season, which removed both of the frontier's principal raiding leaders in a single year.
Petronas was made magistros and celebrated in a triumph, and he died two years later, in 865.
Melitene survived as a city and an emirate but never again mounted a campaign of the kind Umar had made routine. The Paulicians of Tephrike lost their most useful ally and were destroyed as a power within a decade.
The wider consequence took longer to become visible. From the 860s the empire began raiding across the Taurus rather than absorbing raids from it, and the frontier cities that had launched a century of invasions — Melitene itself in 934, then Cilicia, Antioch and Aleppo — were taken one after another in the tenth century.
Lalakaon is the hinge of the Arab–Byzantine wars. Before it the empire is on the defensive everywhere in the east, and its best outcome is a raiding army destroyed on its way home. After it the empire is the aggressor, and it stays that way for a hundred and fifty years.
The reason is only partly the battle. Byzantine recovery met Abbasid disintegration at exactly this moment, and the frontier emirates that had once been the sharp end of a united caliphate were left to face a reorganised empire on their own.
It also matters for how the reign of Michael III is judged. He was not present and did not command, but the victory belongs to his reign, along with the mission of Cyril and Methodius to the Slavs in the same year — and both are routinely lost behind the nickname his enemies gave him.
The main accounts are the continuators of Theophanes and the chronicle of John Skylitzes, with Arabic notices of the emir's death, and they agree on the encirclement, the date and the outcome.
The Byzantine sources were written under the Macedonian dynasty founded by the man who murdered Michael III, which colours the treatment of the reign around the battle but not of the battle itself: Petronas was the new dynasty's kinsman by marriage and there was no reason to diminish him.
One correction is worth stating, because it recurs in popular accounts. The admiral Nasar belongs to the naval campaigns of the 880s and had nothing to do with the Lalakaon; the confusion comes from compressing the whole of the ninth-century recovery into its most famous battle.