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.