Valens (328-378) was the brother of Valentinian, and lived in his brother's shadow for many years. When his brother was appointed emperor in 364 CE, he chose Valens to serve as co-emperor, obtaining the eastern provinces of the Roman Empire. Valens made Constantinople his capital.

Valens was soon presented with a usurper named Procopius in 365, a surviving relative of Emperor Julian who proclaimed himself emperor in Constantinople while Valens was away. He managed to defeat Procopius in the spring of 366, executing the usurper. He then warred against the revolting Goths, before heading back east to face the Sassanid Empire. A resurgent Gothic presence, alongside Huns and Alans, led to the commencement of the Gothic War, after an attempted resettlement of Goths had resulted in them revolting in 377.

Rather than wait for his nephew and co-emperor Gratian to arrive with reinforcements as advised by many, Valens marched out on his own. Valens was struck down during the decisive but avoidable Battle of Adrianople. He was known by some as the 'Last True Roman', and the battle that resulted in his death was considered the beginning of the collapse of the decaying Western Roman Empire.