King of Persia (531–79), whose reign, after a long period of turbulence, marked the highest point of the Sassanian empire. Khosrau I restored royal authority over the army, bureaucracy, and lower nobility, reformed taxation, and restored defences and public works. He invaded Byzantine Syria in 540 and took Antioch. In 565, in alliance with the western Turks, he destroyed the Hephthalite empire on his eastern frontier. He also annexed Yemen and died during negotiations with Byzantium over his invasion of Mesopotamia.