Valentinian I ruled all of Rome for barely a month, then split it
When Roman officials met at Nicaea in 364 to replace a mysteriously dead emperor, one candidate kept refusing, another seemed too boorish and a third lived too far away. They settled on a Pannonian officer who happened to be nearby. Within weeks Valentinian handed the eastern half to his brother and took the West.
Valentinian was born in 321 at Cibalae, today Vinkovci in Croatia, the son of Gratianus, an army officer famed for his wrestling who later served as a count in Africa and Britain before being accused of embezzlement. The family estate was confiscated under Constantius II for supposedly hosting the usurper Magnentius. Valentinian's own career hit a wall under the pagan emperor Julian: accounts disagree over whether he refused to offer pagan sacrifices and left, or was simply dismissed for being Christian.
Julian's successor Jovian trusted him enough to give him an elite infantry command, but Jovian died before reaching Constantinople. Valentinian accepted the throne in late February 364 and faced nervous soldiers who threatened to riot during his first speech; he calmed them by promising the army would be his top priority. On 28 March 364 he made his brother Valens co-emperor in Constantinople, clearly as the junior partner, making Valentinian the second-last emperor to govern the entire empire alone, however briefly.
His reign was spent defending frontiers. When the Alamanni crossed the Rhine in 365 just as a rebellion broke out against Valens in the east, Gallic cities begged him to stay, and he did. After early defeats, his general Jovinus drove the invaders from Gaul, and in 368 Valentinian led a huge army across the Rhine with his eight-year-old son Gratian. He tried, clumsily, to set the Burgundians against an Alamannic chieftain, and sent Theodosius the Elder to crush a revolt in Africa and the Great Conspiracy, a combined assault on Roman Britain by Picts, Scoti and Saxons.
He strengthened border forts along the Rhine and Danube and fought the Quadi and Sarmatians. His end came suddenly, on 17 November 375, when he suffered a fatal stroke while meeting envoys of the Quadi in Pannonia. He founded the Valentinian dynasty and is sometimes called Valentinian the Great.
Source: Valentinian I
