The Battle of Manzikert is fought between the Byzantine Empire and the Seljuq Turks on August 26, 1071 near Manzikert (modern Malazgirt in Muş Province, Turkey).

The decisive defeat of the Byzantine army and the capture of the Emperor Romanos IV Diogenes playsan important role in undermining Byzantine authority in Anatolia and Armenia, and allows for the gradual Turkification of Anatolia.The brunt of the battle is borne by the professional soldiers from the eastern and western tagmata, as large numbers of mercenaries and Anatolian levies flee early and survive the battle.

The fallout from Manzikert is disastrous for the Byzantines, resulting in civil conflicts and an economic crisis that severely weakens the Byzantine Empire's ability to adequately defend its borders.

This leads to the mass movement of Turks into central Anatolia—by 1080, an area of 78,000 square kilometers (30,000 sq mi) will have been gained by the Seljuk Turks.

It will take three decades of internal strife before Alexius I (1081 to 1118) restores stability to Byzantium.