In the spring of 1087, news reached the Byzantine court of a huge invasion from the north. The invaders were Pechenegs from the north-west Black Sea region; it was reported that they numbered 80,000 men in all. Taking advantage of the precarious situation of the Byzantines, the Pecheneg horde headed towards the Byzantine capital at Constantinople, plundering the northern Balkans as they went. The invasion posed a serious threat to Alexios's empire, yet due to years of civil war and neglect the Byzantine military was unable to provide the emperor with enough troops to repel the Pecheneg invaders. Alexios was forced to rely on his own ingenuity and diplomatic skill to save his empire from annihilation. He appealed to another Turk nomadic tribe, the Cumans, to join him in battle against the Pechenegs. Around 1090 or 1091, Emir Chaka of Smyrna suggested an alliance with the Pechenegs in order to completely destroy the Byzantine Empire.^[10]

Won over by Alexios's offer of gold in return for aid against the Pechenegs, the Cumans hurried to join Alexios and his army. In the late spring of 1091, the Cuman forces arrived in Byzantine territory, and the combined army prepared to advance against the Pechenegs. On Monday, April 28, 1091, Alexios and his allies reached the Pecheneg camp at Levounion near the Hebros River.

The Pechenegs appear to have been caught by surprise. At any rate, the battle that took place on the next morning at Levounion was practically a massacre. The Pecheneg warriors had brought their women and children with them, and they were totally unprepared for the ferocity of the attack that was unleashed upon them. The Cumans and the Byzantines fell upon the enemy camp, slaughtering all in their path. The Pechenegs quickly collapsed, and the victorious allies butchered them so savagely that they were almost wiped out. The survivors were captured by the Byzantines and taken into imperial service.

Levounion was the single most decisive victory achieved by a Byzantine army for more than half a century. The battle marks a turning point in Byzantine history; the empire had reached the nadir of its fortunes in the last twenty years, and Levounion signalled to the world that now at last the empire was on the road to recovery. The Pechenegs had been utterly destroyed, and the empire's European possessions were now secure. Alexios had proved himself as the saviour of Byzantium in its hour of need, and a new spirit of hope began to arise in the war-weary Byzantines.