According to some, his good dispositions lasted only during the time that he enjoyed the counsel and support of Abu-zurd-mihir, one of the best advisers of his father; but when this venerated sage was compelled by the infirmities of age to quit his court he fell under other influences, and soon degenerated into the cruel tyrant which, according to all the authorities, he showed himself in his later years.
Meanwhile, however, he was engaged in important wars, particularly with the Roman emperors Tiberius and Maurice, who, now that the great Chosroes was dead, pressed upon Persia with augmented force, in the confident hope of recovering their lost laurels.

On the first intelligence of the great king's death, Tiberius had endeavored to negotiate a peace with his successor, and had offered to relinquish all claim on Armenia, and to exchange Arzanene with its strong fortress, Aphumon, for Daras; but Hormisdas had absolutely rejected his proposals, declared that he would surrender nothing, and declined to make peace on any other terms than the resumption by Rome of her old system of paying an annual subsidy.

The war consequently continued; and Maurice, who still held the command, proceeded, in the summer of A.D.579, to take the offensive and invade the Persian territory.

He sent a force across the Tigris under Romanus, Theodoric, and Martin, which ravaged Kurdistan, and perhaps penetrated into Media, nowhere encountering any large body of the enemy, but carrying all before them and destroying the harvest at their pleasure.

In the next year, A.D.580, he formed a more ambitious project.