Valens was born around AD 328, as the second son of a native of Cibalae in Pannonia called Gratianus.
Alike his brother Valentinian he made a military career. He eventually came serve under Julian and Jovian in the household guard.
Had there been previous divisions of the empire into eastern and western parts, then it had always been eventually unified again. This division though between Valentinian and Valens proved to be final. For a short time the empires should run in harmony. And indeed under Theododius they would even be briefly reunited again. Though it was this division which is seen as the defining moment when east and west established themselves as separate realms.
However much easier the task in the east seemed at first, serious problems soon arose. Was Valens married to Albia Domnica then her father was Petronius, a man widely despised in Constantinople for his greed, cruelty and ruthlessness. So deep seated was the loathing that in AD 365 it even came to a revolt against the emperor and his hated father-in-law.
In AD 366 the forces of Procopius and Valens met at Nacolea in Phrygia. Procopius was betrayed by his generals who deserted him and once he fled he was betrayed yet again and executed.
His position as emperor of the east alas secured, Valens now turned to the threats facing his empire from the north. For the Visigoths, who had already lent Procopius their assistance, were becoming an ever greater threat to the Danubian provinces. Valens countered this threat by crossing the Danube with his troops and devastating much of their territory in AD 367 and then in AD 369 once more.
Thereafter Valens was occupied by troubles arising in the east. Among other things was a conspiracy surrounding a certain Theodorus, which needed to be dealt with in Antioch during AD 371/2.
In AD 375, at the death of his brother Valentinian, Valens assumed the rank of senior Augustus over his nephew Gratian in the west.
Valens was not to show the religious tolerance of his brother in the west. He was a vehement follower of the Arian branch of Christianity and actively persecuted the Catholic church. Some bishops were banished other members of the church met their death.
Next Valens attacked the Persians, though despite achieving one victory in Mesopotamia, hostilities soon ended in another peace treaty in AD 376, neither of the two sides being able to make much of an impression on the other by force of arms.
But then events begun unfolding which should lead to disaster. In the same year as the peace treaty with the Persians, AD 376, the Visigoths came flooding across the Danube in unbelievable numbers.
What followed was a disaster from which the Roman empire would never recover. Valens permitted the Visigoths to settle in the Danubian provinces in their hundreds of thousands.
Valens rushed back from Asia to deal with this terrible crisis. He called upon Gratian to come to his support, yet the western emperor had trouble of his own dealing with the Alemanni. Though once Gratian had freed himself from the immediate menace of the Alemanni, he sent word to Valens that he was coming to his aid and he indeed did mobilize a force and begin marching east.