Which battle in 1071 was a major Byzantine defeat by the Seljuk Turks?

The Battle of Manzikert was the major Byzantine defeat by the Seljuk Turks in 1071.

The battle took place on 26 August 1071 near Manzikert, in eastern Anatolia, between the Byzantine army led by Emperor Romanos IV Diogenes and the Seljuk forces commanded by Sultan Alp Arslan. The Seljuks won after using mobile cavalry tactics, feigned retreats, and coordinated attacks against a Byzantine army weakened by desertions and internal divisions.

Romanos IV was captured, an extraordinary event because he was a reigning Byzantine emperor taken prisoner by a Muslim commander. Alp Arslan treated him relatively generously, and the two rulers negotiated terms before Romanos was released. The immediate territorial consequences were less dramatic than later legends sometimes suggest, but the defeat was followed by a Byzantine civil war that severely weakened imperial control.

Manzikert opened the way for increased Turkic migration and settlement in Anatolia. It therefore became a landmark in the gradual transformation of the region, although historians caution that the battle alone did not instantly destroy Byzantine power there. Myriokephalon was another major Byzantine-Seljuk defeat, but it occurred in 1176, not 1071.