Valentinian I (321–375)

Roman emperor, AD 364–375. He was an able and wise ruler who exercised religious tolerance. He appointed his brother Valens to look after the eastern part of the empire, while he concentrated on guarding its northern and western frontiers, which twice came under serious threat from the Alemanni (in 366 and 368). By fortifying Roman defences along the Danube and the Rhine, he succeeded in repulsing the invaders.