What were the reasons for the defeat of the Emperor Julian the Apostate's invasion of Persia in 363 AD

A coin with a portrait of Emperor Julian

Emperor Julian (331-363 AD), known as Julian the Apostate, was one of the most important Emperors in the history of the Later Roman Empire. He was the last non-Christian to rule the vast territories of Rome. Originally a Christian, he renounced his faith and began to worship the old polytheistic gods of the Roman and the Greek pantheon. This led to him being called an apostate or one who abandoned his religion by the Christians. Julian wanted to halt the Christianization of the Empire and revoked many of the rights of the Church.

The Emperor was an able man, a gifted administrator, and a soldier. It seemed that he would change the Roman Empire, but his disastrous invasion of Sassanian Persia was to end all his ambitions. His defeat virtually ensured that Christianity would triumph in the Roman Empire. Julian's invasion was overambitious and subject to a series of poor strategic decisions resulting in the Emperor's defeat and death.


The acclamation of Julian as Caesar in Paris

Julian was a member of the Constantinian dynasty and a descendant of Constantine the Great. He was one of the few male members of his family who survived a massacre ordered by Constantinus III. Later while still a young man, he was promoted to the rank of Caesar. In 355 AD, he inflicted a series of defeats on Alamanni and Franks, invaded Gaul. His most significant victory was over a great confederation of German tribes in 357 A.D. at the Battle of Argentoratum. After the death of Constantius III, Julian became the sole Emperor of the Roman Empire.

Unlike the other members of the Constantinian dynasty, he was a pagan. Julian was a philosopher, and under the influence of Neo-Platonist philosophy, he began to revere the Olympian Gods. He was brought up a Christian but believed that this religion was undermining the traditional Roman values', weakening the Empire.[1] After assuming the purple, he marginalized the Christian Church and favored pagans. For example, he restored many temples. Julian was careful not to persecute the Christians as he knew that previous persecutions had only strengthened that religion. The Christians hated him.

Julian championed the ancient religion of Rome and Greece in a series of polemics. In his polemic 'Against the Galileans,' he claims Christianity was a series of falsehoods. In one section of the work, he stated," I was convinced that the fabrication of the Christians is a fiction of men composed by wickedness.' [2] There is some evidence that his efforts to promote paganism did have some impact. The Emperor also favored the Jews.

However, the Christians remained as powerful as ever, despite the change in Imperial policy. Some argue that Julian did not want to destroy Christianity but ultimately wanted to see the fusion of the Christian faith with the pagan polytheistic religion. Julian was a great administrator, and he reformed the court, bureaucracy and granted more powers and privileges to the cities.[3]

In 363 AD, the Emperor decided to launch a massive invasion of Persia. Many argue that there were sound strategic reasons for the proposed invasion. Persia under the Sassanian dynasty was a mighty enemy and had secured the strategic initiative on Rome's Eastern Frontier. The pagan sources, such as Ammianus, state that Julian invaded Persia to conquer the Persian Empire.[4]

It is almost certain that Julian wanted to occupy large parts of Persia or to turn it into a puppet regime, as he brought a claimant to the Sassanian throne with him during his invasion. Another motive for Julian's invasion was to emulate the achievement of Alexander the Great. The Emperor's main goal was to re-establish the old Graeco-Roman polytheistic religion. Julian's invasion of the Persian territories could be interpreted as an attempt to secure a victory that would persuade the Romans' to return to their old gods and abandon Christianity.

Invasion of Persia

Emperor Julian's army invaded the Sassanian Empire in 363 A.D. This was the last major invasion of Persia by Rome. Julian prepared meticulously for the invasion of the Sassanian realms. He re-organized the legions of the East and turned them into formidable fighting units. Julian also brought with him experienced legionnaires from the west. Julian created a flotilla of ships to carry his legions deep into Persian territory and to supply his forces.[5] This was an innovative strategy.

Julian conducted the early stages of the invasion very impressively. He had asked Armenia, his ally, to concentrate a significant force on their mountainous border with Persia. This maneuver convinced Persia that Rome would invade via the highlands of Armenia. Many previous Roman armies had followed this route. In this terrain, the Roman legionnaires had the advantage over the formidable Persian cavalry, especially the famed horse archers. In a daring move, Julian invaded through the Syrian desert and followed the route of the Euphrates River.

The Persian Shah Shapur II had been deceived by Julian and was unprepared for the invasion. Julian dispatched a decoy force under Procopius into Persian territory to further confuse Shapur II and his court. Julian's forces advanced rapidly, and he forced the Sassanian king to retreat. The flotilla allowed a large body of troops to be provisioned. Julian feigned a march towards the Tigris, hoping to draw into a battle.

At this time, he divided his forces, and a large army under Procopius invaded Mesopotamia. Upon reaching Carrhae, the main Roman force under Julian turned south and rejoined the transport fleet to begin the main invasion. Its goal was to capture the Sasanian winter capital of Ctesiphon.[6] If Julian captured the city, he would have shown that paganism had restored Rome to greatness. It would also force the Sassanian Shah to the East and ensure not attacking the Roman frontier. Julian defeated a large Persian army on the outskirts of Ctesiphon's city, and he besieged it.

However, he failed to take the city and quietly abandoned the siege, and he burned his flotilla of ships and marched to meet up with the army of Procopius. Many argue that he should have retreated to Syria and abandoned Procopius, but Julian was honorable. He joined up with the other army, and they made their way north to reach Armenia. The Persians constantly harried the Romans and inflicted heavy casualties.[7] It appeared that Julian's army, the largest possibly ever assembled for an invasion of Persia, was about to be destroyed.

The two armies clashed at Samarra now in Northern Iraq, but the battle was inconclusive. However, Julian was wounded, and he died three days later. His successor Jovian saved the army with a peace treaty and was forced to pay tribute to the Persians. Julian's policies that favored paganism were quietly abandoned, and within decades paganism was outlawed by Emperor Theodosius the Great.

Flawed Planning

ruins of Ctesiphon from a 19th century drawing

At first, it appeared that Julian was waging a brilliant campaign, and he was undoubtedly a talented strategist. Julian failed to appreciate the level of resistance as he advanced on Ctesiphon. This was a critical mistake and resulted in Julian losing the initiative.

The resistance on the route to Ctesiphon allowed the Persian Shah Shapur II to gather his forces and assemble a large army. The other great mistake was that Julian had divided his forces, a fundamental and unforgivable error. He ordered Procopius to advance into Mesopotamia, but this achieved little and only weakened his army. After the failure to take the winter capital of the Persians, Julian, instead of retreating to safety in Syria, had to rescue the army of Procopius. [8] If Procopius forces had been with the main force, Julian could have forced a retreat down the Euphrates with his fleet of ships in support.

Instead, the Emperor was obliged to move towards the Tigris, right into the heart of Persia. It was during this effort to contact Procopius that the Battle of Samarra took place. In this, Julian was wounded, and he later died of his wounds. This ultimately led to his army becoming stranded in Persian territory. Furthermore, Julian did not have the technical capability to engage in a lengthy siege of the Sassanian capital.

There were very few siege engines with the army, such as a battering ram or a ballista. Ammianus asserts that Julian hoped that an overwhelming show of force would persuade Ctesiphon to surrender in his histories.[9] This was a mistake, and the Persians defended the walls of their city fiercely. This was another misjudgment of Julian and typical of the wishful thinking that characterized the entire campaign.

Overambitious planning

Sassanian relief showing the victory of Shapur II over Julian

Julian had taken a member of the Sassanian Royal Family who had long been in exile in Rome with him on Persia's invasion. This was to place him on the throne, as Shah presumably. He had been a long-term ally of Rome, and as Shah, he would have been a client king. This was something that Trajan has accomplished in the 2nd century A.D. If Julian had placed his ally on the throne, Persia would no longer be a threat to Rome, and it would be ruled by a monarch who was dependent on Rome.

Julian displayed a lack of knowledge of Persian in his planning for the invasion, especially in believing that he could place an ally on the Persian throne. The Roman army would never have been able to occupy such a vast territory with a fiercely independent population.[10] Julian's plans for the invasion of Persia and his campaign objectives were based on unrealistic assumptions and a fundamental misunderstanding of that Empire. Rome had been in decline and no longer had the resources it once had.

The Romans had failed to conquer Persia, even when it was more robust under the great Emperor Trajan in the second century A.D., Julian did not seem to understand that his Empire was no longer the force that it once was and that his grandiose schemes were unrealistic and even delusional.

Superstition of Julian

It is agreed in the pagan and the Christian sources that Julian did not take his generals' counsel in the planning of the invasion of Persia. It seemed that the Emperor was never willing to take advice, and he trusted his judgments. The Panegyrist Liberanus praised Julian for not 'holding council with his generals but with the gods.' [11] This would indicate that Julian was more interested in omens and portents than his generals, practical advice. The Emperor visited a shrine and received some prophecies, which he did not share with Syria before the invasion.

The reference by Liberanus may also indicate that Julian saw the invasion in a religious and mystical light. He was too readily guided by his religious beliefs rather than by the reality on the ground. Julian was very religious,' and he may have believed that he was divinely favored. This is very much conveyed in his writings when he constantly referred to his guiding spirit.[12] Julian's religious beliefs may explain some of his grievous mistakes as they appear to have clouded his judgment.


Julian's handling of the invasion of Persian was disastrous. He had unrealistic ambitions and objectives, and his planning was not based on the practical challenges involved. He was possibly too eager to achieve a spectacular victory to revive traditional religions, which may have led him to make basic mistakes.

Julian made several strategic decisions that undermined his invasion. The Emperor failed to predict the extent of the resistance of the Euphrates route to Ctesiphon, and unbelievably he failed to prepare for a siege of Ctesiphon. Then he had divided his forces, which was contrary to military doctrine at the time and since.

Julian's handling of the invasion was poor. After the failure of his siege of Ctesiphon, Julian was obliged to link up with Procopius's force, which led to his death and left the Roman army in a precarious strategic position. This resulted in Julian making several miscalculations that probably meant that his defeat in Persia was inevitable. The disaster in Persia in 363 AD ensured that Christianity's rise in the Roman Empire was unstoppable.


  1. Grant, Michael. The Roman Emperors (New York: Barnes and Noble Books, 1997), p. 254
  2. Julian, "Against the Galileans," 143
  3. Grant, p. 255
  4. Ammianus, Histories, v.11
  5. Tougher, Shaun. Julian the Apostate. Edinburg, Edinburgh University Press. 2007), p. 27
  6. Tougher, p. 113
  7. Murdoch, Adrian, The Last Pagan (UK: Sutton Publishing Limited, 2003), p. 113
  8. Murdoch, p. 118
  9. Ammianus, vi, i
  10. Grant, p. 257
  11. Libanius, Oration 18, 306
  12. Grant p. 118

Updated December 4, 2020