The Battle of Köse Dağ took place in eastern Anatolia on 26 June 1243 when an army of the Sultanate of Rum, led by Sultan Kaykhusraw II, confronted an invading Mongol army under the general Baiju and was decisively defeated. The battle was the pivotal event of the Mongol conquest of Anatolia: Rum, previously a significant independent power in the eastern Mediterranean, was reduced to the status of a client kingdom, and its territories were later absorbed into the Mongol Ilkhanate.