Khosrow I (Khosrow Anüshirvan) (khŏsrō´; ănōōshĬrvän´), d. 579, king of Persia (531–79), greatest of the Sassanid, or Sassanian, monarchs. He is also known as Chosroes I or Khosru I. He succeeded his father, Kavadh I, but before becoming king, Khosrow was responsible for a great massacre (c.528) of the communistic Mazdakites. He extended Persian rule E to the Indus River with the capture (560) of Bactria, W across Arabia by establishing (570) at least nominal rule over Yemen, and north and northwest by taking part of Armenia and Caucasia from the Byzantine Empire. He fought against Belisarius and the other generals of Justinian I and against Justin II. Khosrow is revered by the Persians as a just though despotic ruler who encouraged learning, stimulated commerce, rebuilt cities, and set up a reformed system of taxation.