After the battle of Pharsalus, he was commissioned to transport some recently levied troops to Illyricum.
As emperor of the West, Valentinian took Italy, Illyricum.
They made Milan their home; and the empire was nominally divided between them, Gratian taking the trans-Alpine provinces, whilst Italy, Illyricum in part, and Africa were to be under the rule of Valentinian, or rather of his mother, Justina.
As soon as it was known that the armies of the East, Dalmatia and Illyricum had declared for Vespasian, Vitellius, deserted by many of his adherents, would have resigned the title of emperor.
In 39 6 he fought in Greece against the Visigoths, but an arrangement was effected whereby their chieftain Alaric was appointed master of the soldiery in Illyricum (397).