On 29 April 1091 Alexios I, with forty thousand Cuman allies, annihilated the Pecheneg host at Mount Levounion. Anna Komnene wrote that an entire people was destroyed in a single day.
In the spring of 1091 the Byzantine Empire was closer to collapse than at any time since 717. The Seljuks held Anatolia, a Norman invasion had been beaten off at ruinous cost, and a Pecheneg host was wintering inside Thrace within a few days' march of the capital, in alliance with a Turkish emir whose fleet was in the Aegean.
Alexios I had no army capable of meeting them. What he had was diplomacy, and he used it: he hired the Cumans, the steppe people who had pushed the Pechenegs west in the first place, and brought forty thousand of them into Thrace.
On 29 April the combined force attacked the Pecheneg camp at Levounion. What followed was not a battle so much as an extermination, and Anna Komnene — the emperor's daughter, and the source for all of it — recorded it in those terms.
The Pechenegs had crossed the Danube in force from the 1040s and had beaten Byzantine armies repeatedly. By 1090 they had wintered south of the Balkan range and were operating in Thrace as a permanent presence rather than a raid.
Alexios had been emperor for ten years and had spent them on other emergencies: the Norman invasion of the Balkans under Robert Guiscard, the loss of Anatolia to the Seljuks, and a currency collapse.
The Pecheneg alliance with Tzachas, the Turkish emir of Smyrna, was what made 1091 an existential year rather than a bad one. A coordinated attack by land and sea on Constantinople was a real possibility, and the empire had no field army to prevent it.
The Cumans and the Pechenegs were both Turkic steppe peoples, and the Cumans had driven the Pechenegs off the Pontic grasslands a generation earlier. Alexios's proposal was that they finish the job on Byzantine soil, for pay.
Anna Komnene describes the negotiation with some anxiety: forty thousand Cuman horsemen inside imperial territory were an enormous risk, and the emperor spent much of the campaign managing allies who might have changed sides for a better offer.
The gamble is the reign in miniature. Alexios had no army, so he bought one, and he spent the next decade doing versions of the same thing — including, four years later, the appeal to the west that produced the First Crusade.
The armies met on 29 April at the hill of Levounion, near the mouth of the Hebros in Thrace. The Pechenegs were encamped with their families and their wagons, in the steppe manner.
The attack went in at dawn and the camp was overrun. The killing continued into the evening and included the non-combatants, and the Byzantine and Cuman forces then massacred a large number of prisoners during the night — an act Anna Komnene reports and does not defend.
Her summary is the sentence the battle is remembered by: an entire people was destroyed in a single day.
The Pechenegs ceased to exist as an independent power. The survivors were settled inside the empire and enrolled as troops, and Pecheneg units appear in Byzantine armies for the next century.
The Cumans were paid and went home, and they remained a factor on the Danube — sometimes allies, more often not — for the next hundred and fifty years.
A Pecheneg remnant that had stayed north of the Danube crossed again in 1122 and was destroyed by John II at Beroia. After that they disappear from history as a distinct people.
Levounion is the point at which Alexios's reign stops being a holding action. The immediate threat to the capital was gone, the Balkans were secure for the first time in decades, and the recovery that carried the Komnenian dynasty through the twelfth century begins here.
It is also the clearest example in this archive of the steppe frontier working as a system rather than a line: the empire did not defeat the Pechenegs so much as arrange for another steppe people to do it, which is precisely the policy Constantine VII had set out in the De Administrando Imperio a century and a half earlier.
Four years later Alexios sent the appeal west that produced the First Crusade — a request for mercenaries that arrived as an army of conquest, and a reminder that hiring other people's soldiers does not always end as well as it did in 1091.