.. Galla was
afterwards married to Theodosius the Great, who had by her a daughter
named Placidia."

This story, romantic as it is, lacks all the hallmarks of credibility.
In the first place, there is absolutely no trace of this remarkable law
either in the codes or in other historians. Furthermore, the ancient
Church was more severely opposed to bigamy and polygamy than it was to
any other deviation from common morals. Also the Roman law strongly
discountenanced plurality in marriage. Moreover, we have it on the
authority of Ammianus, who is a most trustworthy witness, that
Valentinian was remarkable for his chastity, both at home and abroad.
Also in contradiction to what Socrates relates, Zosimus asserts that
Justina had already been married to Magnentius, and that the emperor was
joined to her in matrimony after the death of Severa, his first wife.
Either this latter statement must be accepted as the fact in the case,
or we must believe that the first empress was divorced, a procedure that
was certainly not difficult and was extremely customary for the rulers
of Rome. What is probably the truth of the matter is that this story of
Justina being the partner of Valentinian in bigamy was a malicious
invention; possibly the discredit of its promulgation should be laid at
the door of some of the Unscrupulous among the orthodox, who were
incensed at her support of heresy.

It was customary for the empress to accompany her imperial husband in
his military expeditions about the Empire. Apart from other
considerations, this was necessary to her safety and that of her
offspring. Conspirators are apt to perpetrate their designs in the
absence of the ruler against whom they are plotting; and in that case,
the legitimate successor, with his protectors--if within reach--is the
first victim of the ambition or precaution of his father's enemies.
Consequently, it was usual for the emperors to take their families with
them even in the most distant journeys. The advantage of this was
illustrated in the death of Valentinian. He had marched against the
Quadi who were vexing the frontier on the bank of the Danube. In his
customary cruel manner, he put to death all who fell into his power,
murdering even the women and children. The desperate people sent envoys
begging for peace and forgiveness, but Valentinian broke out upon them
in one of those paroxysms of rage to which he was subject, and, in the
midst of his terrible invectives, ruptu