When Diocletian appointed a colleague for himself, a second "Augustus," he, as we saw, took the Eastern command for himself and gave the Western to the colleague. When Valentinian finally divided the Empire between himself and his brother Valens, he took the West and gave the East to his brother. It is possible that he may have foreseen something of the trouble that was soon to come on that eastern side. Within three years of his accession to the throne of Constantinople Valens was called upon to lead his legions to repel a great incursion of the Goths. He met them at Adrianople and suffered a terrible defeat. He himself was killed in the battle. The barbarians pressed on. They were at the walls of Constantinople.
Barbarian tribes
A hundred years before this, Goths, crossing the Danube, had fought and conquered Roman legions and had killed an Emperor, namely Decius, who is notorious for his cruel persecution of the Christians known in history as "the Decian persecutions." The Goths had at this time been checked by further Roman forces that were brought against them, but it was then that the Empire lost the province of Dacia, which lay north and east of the Danube, and the Danube thereafter became the boundary.
Now the children of these Goths, rather more than a hundred years later, were across the Danube again, had again conquered the legions and again a Roman Emperor had been slain by them in battle. Constantine had himself been forced to fight the Goths in Thrace, and, when building his new capital, had encircled it with defensive walls. It was well for his successors that he did so. The Gothic army was held before the walls. A large number of their nation had already crossed the Danube and had been admitted as peaceful settlers within the bounds of the Empire. It is certain that Gothic invaders from north of the Danube would find many friends, for the Goths already settled in the Empire were dissatisfied with their treatment by the Romans. And even in the Roman legions that they defeated there would be many of their countrymen, for the recruiting of barbarians among the legionaries had been going on for more than one century. Theodosius the Great, who had succeeded Valens, killed by the Goths, as Emperor of the East, made a treaty with the conquerors, which was faithfully observed until the death of Theodosius in 395. But then the Goths threw off the yoke which the treaty had put upon their necks.
It was fortunate indeed for the Empire that the Persians were no longer a danger on the eastern boundary. A peace with that nation had been arranged in 364, and was not broken for nearly 150 years.
The Goths were divided into several different tribes, not always at peace with each other; and especially into Visigoths and Ostrogoths—that is Western Goths and Eastern. They were so completely divided by the end of the fourth century that the Ostrogoths had fallen under the domination of the Huns, while the Visigoths, further westward, were independent of that fierce and strange people.
But even these Western Goths felt the pressure, pushing them westward, of the Hun, though not so directly. They had the Ostrogoths in between, and sometimes we actually find the Ostrogoths, with the Huns, fighting against the Visigoths. Thus intermixed was the fighting.
And you should know too that although the Romans still called these nations barbarians, many barbarians had come to high honour and great power in one or other of the Roman cities. The division between Roman and barbarian was not nearly so distinct and sharp as the word "barbarian" suggests to us. It was not possible that there should be much idea of inequality between them, seeing that the barbarian could hold such high honour in the chief places of the Empire.