Khosrau I, "the Blessed" (Anushirvan), (531 - 579) was the favourite son and successor of Kavadh I, and the most famous of the Sassanid kings.

According to one account, Khosrau was the Kavadh's son through a peasant girl, and was originally considered unworthy of inheriting his father's throne. His brothers contested his claim, so Khosrau had them killed. At the beginning of his reign he concluded an "eternal" peace with the emperor Justinian, who wanted to have his hands free for the conquest of Africa and Sicily. But his successes against the Vandals and Goths caused Khosrau to begin the war again in 540.

He invaded Syria and carried the inhabitants of Antioch to his residence, where he built for them a new city near Ctesiphon under the name of Khosrau-Antioch or Chosro-Antioch. During the next years he fought successfully in Lazica or Lazistan (the ancient Colchis), on the Black Sea, and in Mesopotamia.

The Romans, though led by Belisarius, could do little against him. In 545 an armistice was concluded, but in Lazica the war went on till 556. At last, in 562, a peace was concluded for 50 years, in which the Persians left Lazistan to the Romans, and promised not to persecute the Christians, if they did not attempt to make proselytes among the Zarathustrians; on the other hand, the Romans had again to pay subsidies to Persia.

Meanwhile in the east the Hephthalites had been attacked by the Turks (Gokturks). Khosrau united with them and conquered Bactria, while he left the country north of the Oxus to the Turks. Many other rebellious tribes were subjected. About 570 the dynasts of Yemen, who had been subdued by the Ethiopians of Axum, applied to Khosrau for help. He sent a fleet with a small army under Vahriz , who expelled the Ethiopians. From that time till the conquests of Mahomet, Yemen was dependent on Persia, and a Persian governor resided here. In 571 a new war with Rome broke out about Armenia, in which Khosrau conquered the fortress Dara on the Euphrates, invaded Syria and Cappadocia, and returned with large booty. During the negotiations with the emperor Tiberius, Khosrau died in 579, and was succeeded by his son Hormizd IV.

Although Khosrau had in the last years of his father extirpated the heretical and communistic Persian sect of the Mazdakites (see Kavadh). He was a sincere adherent of Zoroastrian orthodoxy and even ordered that the religion's holy text, the Avesta be codified, but he was not fanatical or prone to persecution. He tolerated every Christian confession. When one of his sons had rebelled about 550 and was taken prisoner, he did not execute him; nor did he punish the Christians who had supported him.

He introduced a rational system of taxation, based upon a survey of landed possessions, which his father had begun, and tried in every way to increase the welfare and the revenues of his empire. In Babylonia he built or restored the canals. His army was in discipline decidedly superior to the Romans, and apparently was well paid. He was also interested in literature and philosophical discussions. Under his reign, chess was introduced from India, and the famous book of Kalilah and Dimnah was translated. He thus became renowned as a wise prince.

When Justinian in 529 closed the Academy of Athens, the last seat of paganism in the Roman empire, the last seven teachers of Neoplatonism emigrated to Persia. But they soon found out that neither Khosrau nor his state corresponded to the Platonic ideal, and Khosrau, in his treaty with Justinian, stipulated that they should return unmolested.