The Goths meet only light Roman resistance and advance northwest into Dacia in 379, plundering this region.

General Theodosius the Younger, who has remained in retirement in Spain following the execution of his father, had married a fellow Spaniard, Aelia Flacilla, at the end of 376.

Theodosius' first son, the future emperor Arcadius, had been born in 377, and his daughter Pulcheria in January 378.

Immediately after the catastrophic defeat and death of Valens at Adrianople, Gratian unexpectedly summons to his court Theodosius to control the incursions.

When Theodosius once again proves his military ability by a victory over the Sarmatians, Gratian, before the army, proclaims him co-emperor on January 19, 379.

The extremely pious Gratian, having come under the influence of Bishop Damasus or Rome and of Bishop Ambrose of Milan, has chosen Theodosius not only for his military ability but also for his orthodoxy.

His dominion is to be the eastern part of the empire, including the provinces of Dacia (present-day Romania) and Macedonia, taken from Gratian's stepbrother, the augustus Valentinian II, which have been especially infiltrated by barbarians in the preceding few years.

Emperor Theodosius, residing chiefly in Thessalonica, seeks first to rebuild the imperial army, the discipline of which is considerably impaired, and to consolidate Rome's position on the Balkan peninsula.

Military unpreparedness cannot be overcome by conscription alone, which applies only to certain classes.

Theodosius therefore directs that the army accept large numbers of Germans, who had been barred from military service.

Foreigners have by 379, however, already intermingled extensively with the rest of the army, both among the troops and in all ranks of the officer corps, so Theodosius does no more than many of his predecessors to encourage this process.

Both Romans and Germans are among the leading generals in Theodosius' provinces, in contrast to the West.

Theodosius' situation is complicated by the sharp antagonism that arises around 379 between disciples of the Nicene Creed (according to which Jesus Christ is of the same substance as God the Father) and several other Christian groups in his part of the empire.

Gregory of Nazianzus assumes leadership of the orthodox community in Constantinople, a city divided by religious controversy, in 379.

…Jerome goes to Constantinople to pursue his study of Scripture under the instruction of Gregory Nazianzen.

Here he seems to have spent two years.

The anti-Arian bishop Meletius of Antioch remains in exile as ordered by the Eastern emperor Valens.

The bishops of Alexandria and Rome, viewing the presbyter Paulinus as more orthodox than Meletius, had taken the side of the former; Basil of Caesarea had been the latter’s principal supporter.

A further complication had been added when, in 375, the heretical bishop Apollinaris of Laodicea consecrated Vitalius, one of Meletius' presbyters, as bishop.

Meanwhile, under the influence of his situation, Meletius has been more and more approximating to the views of Nicene Creed.

Basil, throwing over the cause of Meletius’ predecessor Eustathius, deposed as an Homousian heretic by the synod of Melitene, championed that of Meletius who, when after the death of Valens he returns in triumph to his diocese, is hailed as the leader of Eastern orthodoxy.

As such, he presides in October 379 over the great synod of Antioch, in which the dogmatic agreement of East and West is established.

Jerome, returning in this year to Antioch, had heard the teachings of Apollinaris and been admitted to the priesthood by Paulinus, apparently with some unwillingness and on condition that he still continue his ascetic life.

Soon afterward, he goes to Constantinople to pursue his study of Scripture under the instruction of Gregory Nazianzen.

Gregory of Nyssa, leader of the orthodox party in controversies over the doctrine of the Trinity, had in 376 been deposed from his bishopric by the Arian party in 376 but restored two years later.

After attending the council at Antioch in 379, he is sent on a special mission to the churches of Arabia (i.e., Transjordan); …

…Gregory’s visit to Jerusalem on this occasion leaves him with a dislike for the increasingly fashionable pilgrimages, an opinion he expresses vigorously in one of his letters.

The Goths, who by 380 can no longer be driven from the empire, divide into Therving and Greuthung armies, in part because of the difficulty of keeping such a large number supplied.

The Greuthungs move north into Pannonia, where Gratian in 380 agrees with a cluster of three tribal armies to settle them on vacant lands as a unit under their own chiefs.

Constantinople’s ascendant orthodox establishment relieves the Arian faction of its churches here in 380.