Valentinian, the son of an army officer…

Valentinian, the son of an army officer stationed in Pannonia, had joined the army and served with his father in Africa.

According to some sources, when Valentinian was a tribune in the forces of Julian, he had been disgraced for refusing to renounce Christianity.

Having served, however, in Julian's Persian expedition, he had been promoted by Jovian.

Nine days after Jovian's death, the commanders of the army proclaim the forty-three-year-old Valentinian emperor at Nicaea (modern Iznik, Turkey).

Once again, the general staff has unanimously chosen a Pannonian officer—an energetic patriot and, like Jovian, a moderate Christian—but he has to yield to the rivalry of the armies by dividing authority.

Valentinian accepts the acclamation on February 26, 364.

As he prepares to make his accession speech the soldiers threaten to riot, apparently uncertain as to where his loyalties lie.

Valentinian reassures them that the army is his greatest priority.

According to Ammianus, the soldiers were astounded by Valentinian’s bold demeanor and his willingness to assume the imperial authority.

To further prevent a succession crisis he agrees to pick a co-Augustus.

His decision to elect a fellow-emperor can also be construed as a move to appease any opposition among the civilian officials in the eastern portion of the Empire.

By agreeing to appoint a co-ruler, he assures the eastern officials that someone with imperial authority will remain in the east to protect their interests.