The Battle of Save occurred in 388 between the opposing troops of the Eastern Roman Empire and Magnus Maximus, who planned to usurp the Roman throne. The Roman Emperor Theodosius I claimed victory over his supposed usurper Magnus Maximus and executed him in the city of Aquileia.

Background

Emperor Gratian reigned over western Rome from April 359 to his death in August 383. His uncle, Valens, died at the Battle of Adrianople in August 378. The death of Eastern Roman emperor Valens led Gratian to appoint Theodosius as his co-emperor with the title of Augustus. Thus Theodosius was his co-emperor, controlling the eastern part of Roman territory. He was assigned to defeat the Goths, who caused an uproar during the Battle of Adrianople and claimed areas on the Roman frontier. 

In 383, many Western Roman citizens grew resentment over Gratian’s preference for his Scythian soldiers over public service. This resulted in a revolt by the British legions, who proclaimed Magnus Maximus as their new emperor. 

Magnus Maximus journeyed to Gaul, where he would kill emperor Gratian to overthrow him, leaving Theodosius with a dilemma. Would he accept Magnus Maximinus as the emperor despite his involvement in killing his former co-emperor, or would he battle against him? Tensions with the Goths still called for manpower in the east, so Theodosius instead agreed that Magnus Maximus would keep the western part of Rome. At the same time, the son of former emperor Valentinian I, Valentinian II, would be co-emperor. Valentinian II was four years old at the time; he reigned over Italy with the guidance of his mother, Justina. 

Four years later, Justina’s religious beliefs in Arianism caused conflicts with the well-liked bishop Ambrose of Milan. The people regarded her unfavorably, which Magnus Maximus saw as an opportunity to take over Italy. He took Italy from the young Valentinian II, who was then 16 years old, making Magnus Maximus the ruler of the entire Western Rome. Valentinian II and his family fled to the east to seek refuge with Theodosius. 

The English historian Gibbon mentioned that Theodosius contemplated whether to go into battle with Magnus Maximus due to the usurper’s strong Germanic support. However, the eastern emperor was convinced to do so for his love, Galla, who was Valentinian II’s sister. Justina was quick to approve of Theodosius and Galla’s union, after which Theodosius headed to war. 

The Battle

In 388, Magnus Maximus had taken Siscia and was on his way to the Save River. He was known for his powerful forces composed of troops from Britain, Gaul, and Spain, as well as Germanic auxiliaries. Meanwhile, Theodosius had the advantage over naval forces with 40,000 Foederati along with auxiliaries which consisted of Alani and Huns. The eastern emperor passed through Illyricum on his way to Magnus while his lieutenant Arbogastes traveled north to Gaul. 

Both forces battled for two months, ending on the Save River. Theodosius’ forces were able to advance through the river and reach the opposite bank. Magnus Maximinus’ brother and lieutenant, Marcellinus, deployed a counter-attack that allowed Magnus’ troops to retreat to the west of the Julian Alps. Magnus stayed at the Aquileia, a fortress in the area. 

Theodosius followed Magnus to Aquileia, and his soldiers laid siege to the fortress. Magnus eventually surrendered and was given to Theodosius in chains. Magnus and his son, Victor, were executed on August 28, 388. Their deaths ended the civil war.