It is about the year 370 that we begin to hear of the Huns. The first people to fall a victim to their eastward aggression were the Alans, next came the Ostrogoths, whose king, Hermanric, was driven to suicide; and by 375 the Visigoths were threatened with a similar fate. Hemmed in by the advancing flood of Huns and the stationary power of Rome this people, after a vain attempt to ally itself with the latter, was forced into arms against her. An indecisive battle with the generals of Valens (377) was followed by a crushing Roman defeat in the succeeding year (August 9, 378) at Adrianople, where Valens himself, but recently returned from his Persian war, lost his life.
Gratian and his half-brother, Valentinian II., who had become Augusti upon the death of their father, Valentinian I., in 375, would have had little power of themselves to withstand the victorious Goths and Rome might well have fallen thirty years before she did, had it not been for the force of character and the military skill of that same Theodosius whose successes against the Alamanni have already been mentioned. Theodosius was summoned from his retirement in Spain and made Augustus (January 19, 379). During the next three years he succeeded, with the help of the Frankish generals, Bauto and Arbogast, in gradually driving the Goths northward, and so relieved the barbarian pressure on the Eastern Empire and its capital. In 381 Athanaric, the Gothic king, sued in person for peace at Constantinople and there did homage to the emperor. In the following year the Visigoths became allies of Rome and, for a time at least, the danger was averted.
Meanwhile the West was faring not much better. Gratian, after an uneasy reign, was murdered in 383 by the British pretender, Magnus Maximus. From 383 to 387 Maximus was joint ruler of the West with Valentinian II., whom he had left in command of Italy rather from motives of policy than of clemency; but in the latter year he threw off the mask and, crossing the Alps, descended upon his colleague whose court was at Milan. Valentinian fled to Thessalonica and there threw himself on the mercy of Theodosius. Once more that general was to save the situation.