AE Follis AE3, AD 367-375, Siscia, 16.7mm, 2.19g, 0°, RIC IX 14a.
Obv: DN VALENTINIANVS PF AVG. Diademed, draped, cuirassed bust right.
Rev: GLORIA ROMANORVM. Emperor advancing right, dragging captive and holding labrum; D in field / BSISC in ex.
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Flavius Valentinianus, commonly known as Valentinian I or Valentinian the Great, was Roman Emperor from 364 to 375. He was the last emperor to have de facto control of the entire empire. Valentinian accepted the acclamation on 26 February 364. As he prepared to make his accession speech the soldiers threatened to riot, apparently uncertain as to where his loyalties lay. Valentinian reassured them that the army was his greatest priority and to further prevent a succession crisis he agreed to pick a co-Augustus. He selected his brother Valens as co-Augustus at Constantinople on 28 March 364.

In 373, hostilities erupted with the Quadi, a group of Germanic-speaking people living on the upper Danube. During the fall, along with their allies the Sarmatians, they crossed the Danube and began ravaging the province of Pannonia Valeria. Two legions were sent in but failed to coordinate and were routed. Valentinian did not receive news of these crises until late 374. The following spring he arrived at Carnuntum, which was deserted where he was met by Sarmatian envoys who begged forgiveness. Valentinian replied that he would investigate and act accordingly. He crossed the Danube into Quadi territory and after pillaging without opposition, he retired to Savaria to winter quarters. In the spring he decided to continue campaigning and moved to Brigetio. Once he arrived, he received a deputation from the Quadi. In return for supplying fresh recruits to the Roman army, the Quadi were to be allowed to leave in peace. However, before the envoys left they were granted an audience with Valentinian. The envoys insisted that the conflict was caused by the building of Roman forts in their lands. The attitude of the envoys so enraged Valentinian that he suffered a stroke that ended his life.

Due to the successful nature of his reign and almost immediate decline of the empire after his death, he is often considered the "last great western emperor". His sons Gratian and Valentinian II succeeded him in the western half of the empire.