The Ecclesiastical History Of Scholasticus by Socrates Scholasticus
Chapter XLIV.--Marriage of the Emperor Valentinian with Eudoxia the Daughter of Theodosius.
He had by the empress Eudocia, his wife, a daughter named Eudoxia. Her his cousin Valentinian, appointed by him emperor of the West, demanded for himself in marriage. When the emperor Theodosius had given his assent to this proposal, and they had consulted with each other as to the place on the frontiers of both empires, where it would be desirable that the marriage should be celebrated, it was decided that both parties should go to Thessalonica (which is about half-way) for this purpose. But Valentinian sent a message to the effect that he would not give him the trouble of coming, for that he himself would go to Constantinople. Accordingly, having secured the Western parts with a sufficient guard, he proceeded thither on account of his nuptials, which were celebrated in the consulate of Isidore and Sinator; after which he returned with his wife into the West. This auspicious event took place at that time.