Battle of the Frigidus River: East Romans Defeat West Romans, Reuniting the Empire

« Previous story
Next story »
Battle of the Frigidus River: East Romans Defeat West Romans, Reuniting the Empire

Roman Empire, c. AD 395, at death of Theodosius
Image courtesy of
(Unless otherwise indicated, all illustrations are courtesy of Wikipedia)

Today in Military History: September 5-6, AD 394

Today's history spotlight falls on a little-known, but no less important, battle which occurred in the late fourth century AD. Besides the on-the-field fighting between armies from the Eastern and Western Roman empires, there was also a subtext of Christian vs. pagan religions, which figured prominently in the conflict's climax.


After Constantine the Great became sole Roman emperor (AD 324), he proclaimed that Christianity was legal and that persecutions of its adherents were to stop. From that time up through the latter part of the fourth century, there was still a strong strain of paganism in the Roman Empire. This was especially true in the Roman Senate, where most of its members were conservative and clung to their old ways. In 380 East Roman Emperor Theodosius I (the Great) issued an edict that essentially declared Nicene Christianity to be the sole religion of both the East and West Roman empires. [There was a substantial population of Arian Christians in both empires, but the Nicene version was gaining ascendancy.]

Theodosius was basically the senior ruler of both empires, and exercised authority over both entities. He appointed a number of officials in the West, including the magister militum (supreme military commander) of the Western Empire, a Frank named Arbogast. This man was also essentially the guardian of Western Emperor Valentinian II, who was only about 18 years old at the time. Very soon, Arbogast began to act like he himself was the Western emperor. At one point, Valentinian attempted to dismiss his Frankish general. Arbogast simply tore up the letter, publically saying since Valentinian had not appointed him, he could not be dismissed by the teen-aged ruler.

On May 15, 392, Valentinian was found hanged to death in his residence in France. Arbogast filed a report on the incident with Theodosius, saying it was suicide. The Frank's report was widely doubted. Upon hearing of Valentinian's demise, Theodosius appointed his son Arcadius as the new Western ruler. Three months later, Arbogast appointed an imperial official named Eugenius – a former teacher of rhetoric – as emperor in the West. [This was obviously a ploy by the Frank to have someone he could control as a figurehead, while he continued as the power behind the throne.]

During that time, the Roman Senate took steps to re-introduce the worship of the old gods in the Western empire. Temples were re-opened and refurbished. In addition, Eugenius appointed his own men to high positions formerly held by officials appointed by Theodosius. When a delegation of officials journeyed to Constantinople seeking the acknowledge of Eugenius's elevation to Western emperor, Theodosius didn't give a definitive answer. He tolerated the usurpation for several months, then in January of 393 he appointed his 8-year old son Honorius to be the Western emperor. As a result, civil war broke out.

Prelude to the Battle

Over the succeeding months, Theodosius and Arbogast marshalled their forces in preparation for a final confrontation on the battlefield. The Eastern Army was still trying to recover from the disaster at Adrianople in 378. [Readers interested in this battle should go to my BurnPit posts from August of 2012: Battle of Adrianople: Goths Destroy East Roman Army and Part II: Battle of Adrianople.] As a result, Theodosius and his military commanders – especially his chief generals Stilicho and Timasius – launched a program of recruitment and conscription to bring the Eastern Army back up to strength. The two men also were given the task of restoring discipline in the remaining legions.

This program was not entirely successful, so Theodosius was forced to recruit large numbers of Visigoths, Germanic barbarians who had been settled in Roman territory south of the Danube River. They were given the designation foederati, men would join the Roman army if needed. The Visigoths would be allies, functioning with their own arms and equipment and under their own leader, named Alaric. Finally, in May 394 the East Roman Army left Constantinople, to make the westward journey to confront the usurper Eugenius and his sponsor Arbogast.

Area of the battle of the Frigidus River, showing defenses of the Claustra Alpium Iuliarum; Map courtesy of Cristiano64 (and Wikimedia Commons)
Area of the battle of the Frigidus River, showing defenses of the Claustra Alpium Iuliarum
Map courtesy of Cristiano64 (and Wikimedia Commons)

The Eastern Army made slow progress marching through the Balkan hills and forests. Theodosius and his generals were cautious, expecting attacks by Western forces normally stationed in Pannonia (which is today part of Slovenia). In fact, the Eastern Army met no opposition on its march. In late August, Theodosius's army began to traverse a section of the Julian Alps, near modern-day Trieste. The Eastern Romans soon discovered that the usually well-defended mountain passes were deserted. [Arbogast had made the decision to concentrate his Western forces united, rather than throw units piecemeal at the invaders.] Finally, the Easten Army began to traverse a section of defenses known as the Claustra Alpium Iuliarum. It consisted of strategically placed palisades and forts, designed as an inner defensive line to stop invasions from the east. But it was similarly deserted. However, in the early days of September, 394 as the East Roman forces were traversing the valley of the Frigidus River (today the Vipava River), descending a narrow mountain pass when they encountered the encampment of the West Roman Army. Both forces rushed to deploy for battle.

East Roman Army

Modern historians estimate the East Roman force's size at about 50,000 men, with Visigothic foederati making up about 40 percent of the total. In addition to troops from nearby Greece and Asia Minor, Stilicho and Timasius called in Roman units from as far away as Syria (probably auxiliaries). There is some speculation they may have cannibalized some of the border guard units in Dacia and Thrace. They may even have recruited some Georgian troops, for a Georgian officer named Bacurius the Iberian is mentioned in chronicles of the time. [Georgia/Armenia was a disputed area to the southeast of the Black Sea, an area that was also claimed by the Sassanid Persian Empire.]

4th century AD Visigothic warrior; Image courtesy of
4th century AD Visigothic warrior
Image courtesy of

It is also possible that additional barbarian foederati were recruited from other nearby tribes, like the Vandals and the Huns, but likely in small groups and not the massive numbers that characterized the Visigothic contingent. One difference between the early Roman armies and those of the late fourth century were a larger reliance on cavalry. While not in the large numbers that characterized the later Byzantine armies, more Roman horsemen were needed to patrol large areas and to move quickly to oppose any external threat. In addition, more heavily armored Roman cavalry were needed against the Eastern Empire's primary enemy, the Sassanid Persians.

West Roman Army

4th century AD Roman legionary (re-enactor); Photo courtesy of
4th century AD Roman legionary (re-enactor)
Photo courtesy of

The Western Roman Army was probably having the same recruitment problems as the Eastern realm, but even more so. Civil administration was beginning to break down, agriculture was not as successful as in previous years, and taxation was not keeping up. The army was starting to recruit large numbers of barbarian foederati, probably in larger numbers than the Eastern Army. With Arbogast in charge of the army, he likely recruited large numbers of his fellow Gallo-Romans. There were still numbers of classic heavy infantrymen, but they were beginning to be outnumbered by the barbarian auxiliaries. Many newer troops were less well armed and armored as previously. As in the Eastern army, cavalry was becoming a larger percentage of the overall number of the Western forces – but not quite in the numbers as in the east. Most modern historians estimate the Western Army to be about the same size and the Eastern force, about 50,000 men.

Battle of the Frigidus River

The two armies were lined up for battle on September 5. If classic Roman formations were still being used, the Western forces lined up with the main Roman infantry formations in two or three lines. Skirmish troops – javelinmen and bowmen – were placed in front of the infantry, with its cavalry units situated on both flanks. In addition, Arbogast had ordered palisades and a ditch dug on the plain in front of the mouth of the pass, and also a heavily fortified camp to the rear of the Western army. The Eastern Army of Theodosius probably used similar formations – with one exception. All of his Visigothic foederati were placed in front of the Roman units.

The battle opened with the Eastern Roman army advancing to attack. The Visigoths were ordered to strike the first blows, and they continued to fight throughout the day. The fighting was bloody. [Histories of the battle claim that Western Emperor Eugenius was present at this battle. He ordered a statue of Jupiter to be placed on the edge of the battlefield to strengthen his men's morale. In addition, Arbogast ordered the army banners to carry various pagan religious symbols. One mentioned prominently was Hercules, which many West Romans also painted on their shields.] The Visigoths made at least two wild charges against the center of the West Roman army. Theodosius likely ordered his Georgian/Armenian troops into battle during the day's fighting, leading to the death of their leader Bacurius the Iberian. By the end of the day, Theodosius's troops were exhausted, and they fell back into the mouth of the pass. Nearly one-half of the Visigothic foederati were killed.

Visigoths (right) charge West Roman center on battle's first day; Image courtesy of
Visigoths (right) charge West Roman center on battle's first day
Image courtesy of

Facing an intolerable situation, Theodosius spent much of the evening in prayer. One historian claims that at one point in the night, two horsemen clad all in white appeared to the Eastern emperor. He viewed this incident as an answer to his prayers.

During the night of September 5-6, Western emperor Eugenius ordered victory celebration in the army camp, sure that the next day the East Romans would be swept from the field. Also that night, Western Roman commander Arbogast sent a substantial portion of his army under the command of an officer named Arbitio to attempt to outflank the Eastern army, block other mountain passes and perhaps attack the demoralized Easterners from the rear. However, when Arbitio and his men made contact with the Eastern Roman force, he defected to Theodosius after agreeing to a considerable monetary inducement. This act was viewed by the Eastern emperor as another answer to his prayers.

As the two armies lined up for a continuation of the previous day's fighting, even though the East Roman Army was now probably larger than the Western forces, Theodosius likely thought he needed another miracle to win the fight against the Western usurper and his puppet master Arbogast. Well, if the various chronicles of the battle can be believed, he received his miracle.

It came in the form of "an indescribably great windstorm [which blew] violently in faces of the enemy." This was a weather phenomena known as the bora, a windstorm that blows down from the mountains, and wreaks havoc on crops, buildings, and people. The storm blew from east to west, directly into the faces of the Western army, showering them with sand, dirt, and grit. It was said to be so strong that it caused the javelins and arrows fired by the West Romans to be blown back toward them. At the least, it disrupted the formations of Arbogast's army, and when the East Romans charged, the battle success of the previous day deserted the West Romans. When one detachment of the West Romans was routed, apparently the remainder of Arbogast's forces disintegrated in the face of the East Romans' attacks. For all intents and purposes, the battle of the Frigidus River was over.


As with many battle of ancient times, casualty figures for this battle are problematic. For the East Roman army, the only number given is that 10,000 Visigoths perished; we can probably guess another 5000 or so deaths for Theodosius's army.

For the Western Roman forces, we can probably use the term "heavy" without contradiction. Arbogast's forces scattered, most probably returning to their places of origin, or some likely surrendering to the East Romans. Many of the West Romans may have perished in the pursuit after the battle. However, Theodosius probably wanted to limit the post-battle slaughter, realizing he needed to reorder the Roman army in the West, and needed warm bodies.

Footnote #1: Within four months of his victory, Emperor Theodosius was dead at the age of 48. He left the two halves of the empire in the hands of his two sons: his 10 year old son Honorius in the West, and his 18 year old son Arcadius in the East. The beginning of the Byzantine Empire – which would last over 1000 years – can be traced to these events.

"Western Roman Emperor Honorius" by Jean-Paul Laurens (1880); Currently at Chrysler Museum of Art, Norfolk VA
"Western Roman Emperor Honorius" by Jean-Paul Laurens (1880)
Currently at Chrysler Museum of Art, Norfolk VA

Footnote #2: Prior to his death in January of 395, Theodosius appointed his general Stilicho (who was half-Vandal, half-Roman) to be the caretaker of the still-underage Honorius. He functioned well as the magister militum in the West. Stilicho defeating the Visigoths – now ruled by Alaric – in several battles, most notably at the battle of Pollentia in 402. As the years passed, he began to assume more power, and his army finally revolted in 408. Stilicho was arrested and executed by his enemies in the Imperial court.

Footnote #3: In the aftermath of the Frigidus River fight, the Western Emperor Eugenius was captured, and beheaded. His commanding general Arbogast fled into the Julian Alps, and eventually committed suicide.

Posted in top stories | 0 comments
« Previous story
Next story »


* To comment without a Facebook account, please scroll to the bottom.

Add new comment

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Have a tip for us? A link that should appear here? Contact us.
News from the World of Military and Veterans Issues. Iraq and A-Stan in parenthesis reflects that the author is currently deployed to that theater.