(1071), battle in which the Byzantines under the emperor Romanus IV Diogenes were defeated by the Seljuq Turks led by the sultan Alp-Arslan. It was followed by Seljuq conquest of most of Anatolia and marked the beginning of the end for the Byzantine Empire as a militarily viable state.

Spurred by Seljuq raids and incursions into Byzantine-ruled Anatolia, Romanus assembled a large army to reestablish the security of the Byzantine Empire's eastern frontier there. In the spring of 1071 he led this army into parts of Turkish-held Armenia, entering Armenia along the southern branch of the Upper Euphrates River. Near the town of Manzikert (present Malazgirt, Tur.), he divided his army, which was composed of mercenaries that included a contingent of Turkmen, sending some ahead to secure the fortress of Akhlât on nearby Lake Van and taking others with him into Manzikert. Learning of the Byzantine foray into his territory, Alp-Arslan hastened to Manzikert, where he confronted the emperor's army.

Romanus abandoned Manzikert in an attempt to reunite his forces with the group besieging Akhlât. Trapped in a valley on the Akhlât road, he neglected to send out scouts to assess the enemy's position, and the Turks fell upon him. Romanus fought valiantly and might have won if his position had not been weakened by treachery within his ranks; his Turkmen troops went over to the enemy the night before the battle, and one of his generals, Andronicus Ducas, perceiving that the cause was lost, fled with his men. The Byzantine army was destroyed, and Romanus was taken prisoner.