Valentinian I ( 321 – 17 November 375), sometimes known as Valentinian the Great, was Roman emperor from 364 to 375. He is the second-last emperor to govern the empire as a whole, albeit only from February to March of 364, after which he appointed Valens to rule over the Eastern half the empire, while he remained in control of the West. The founder of the Valentinian dynasty, he is noted for his successful campaigns on the Rhine and Danube frontiers.