 From his uncle , Justinian inherited ongoing hostilities with the Sassanid Empire . In 530 a Persian army was defeated at Dara , but the next year saw the defeat of Roman forces under Belisarius near Callinicum . When king Kavadh I of Persia died ( September 531 ) , Justinian concluded an " Eternal Peace " ( which cost him 11 @,@ 000 pounds of gold ) with his successor Khosrau I ( 532 ) . Having thus secured his eastern frontier , Justinian turned his attention to the West , where Germanic kingdoms had been established in the territories of the former Western Roman Empire . 
