Posted by Powee Celdran

A Time Traveller’s Guide to Byzantium: 62 Years that Shook and Shaped the Eastern Roman Empire (2025/2026) by content creator Powee Celdran serves as a non-academic, illustrated guide navigating the 1,100-year history of the Empire from 330 AD to 1461.

For four centuries, the Roman and the Sassanid Persian Empires have been in
constant conflict with each other despite moments of uneasy peace in between. Most of the
conflicts between the two powerful empires ended with territorial gains and losses for
either side. Only a few instances during the wars between both empires saw dramatic
events happed such as the capture of the Roman emperor Valerian after his defeat to the
Sassanids at the Battle of Edessa in 260 and the death of Emperor Julian in campaign
against Persia in 363. However, the many wars fought between the Roman and Sassanid
Empires never ended with either side nearly destroying the other until the final war from
602-628 between the Eastern Roman or Byzantine Empire against the Sassanids.

This war, often called the “Last Great War of Antiquity” was the final conflict
between the Romans and Persians and the most devastating one between them. This 26-
year war was no longer a war over borders but one of conquest in which the Sassanids
made major territorial gains conquering the Byzantine Levant, Egypt, and Asia Minor while
even attempting to take the Byzantine capital Constantinople itself.

Although the Sassanids made major territorial gains, the Byzantines under Emperor Heraclius made a daring
counteroffensive into Persian territory and at the end won a costly victory regaining
everything they lost to the Sassanids. Despite the Byzantines’ ultimate victory in this war, it
was exhausted and deprived of troops and thus vulnerable to the new rising power of the
first Islamic Caliphate from Arabia which just a decade after the great war conquered most
of what the Byzantines regained from the Persians in the Middle East and eventually
conquered and ended the Sassanid Empire.

Origins of the War

The origins of the great war of 602-628 go back to the reign of the Byzantine
emperor Maurice (582-602) whose reign saw the culmination of the previous major war
between the Byzantines and Sassanids that originated in 572 when Byzantine emperor

Justin II (r. 565-578) refused paying tribute to the Sassanid emperor Khosrow I (r. 531-
579). This war from 572-591 saw the Byzantines score many military victories over the
Sassanids and culminated with Emperor Maurice restoring the Sassanid ruler Khosrow II to
power in 591 after a combined army of Byzantines and Sassanids defeated the Sassanid
usurper general Bahram Chobin in battle. As Khosrow II- who previously reigned in 590-
regained the throne thanks to Maurice’s intervention, he ceded most of Persian
Mesopotamia as well as most of Armenia and Iberia (Georgia) to the Byzantines all while
the Byzantines were no longer to pay tribute money to the Sassanids.

Having secured an “eternal” peace with the Sassanids, Maurice returned to
campaigning in the empire’s northern frontier in the Balkans by defending it from Avar and
Slav raids from across the Danube. Because the previous war against the Sassanids drained
the Byzantine treasury, Maurice had to implement strict financial policies especially with
the army by cutting their bonuses and having them spend the winter season in campaign
across the Danube both to save money and prevent Avar and Slav raids. This however was
Maurice’s undoing as this policy led to many military mutinies, the most notable one in 602
wherein the army camped at the Danube proclaimed their centurion Phocas as emperor
against Maurice. This mutiny ended in success with Phocas being crowned emperor and
Maurice and his sons captured and executed under Phocas’ orders.

The execution of Maurice in 602 gave his ally, the Sassanid emperor Khosrow II an
excuse to declare war on the Byzantines and this time, he no longer saw it as a war over
borders but one of conquest. Khosrow got the opportunity to invade the Byzantine Empire
in 603 when Narses, the military governor of Byzantine Mesopotamia who was a loyalist of
Maurice declared rebellion against Phocas and requested help from Khosrow II who gladly
accepted the offer. The war thus began with Khosrow invading Byzantine Mesopotamia and
capturing the strategic fortress of Dara in 605. Narses meanwhile returned to
Constantinople hoping to discuss peace terms with Phocas but was instead captured and
burned alive by Phocas.

The Rise of Heraclius

As emperor, Phocas as a centurion having little to no experience in running an
empire focused on purging anyone disloyal to him and his regime instead of the Persian
threat which by this point had already spread across most of Byzantine Asia Minor. Many of

Maurice’s generals and officials were either imprisoned or executed by Phocas who
replaced them with his incompetent relatives. However, Priscus, one of Maurice’s generals
who was retained by Phocas and even becoming Phocas’ son-in-law was secretly
conspiring with the Exarch of Africa Heraclius the Elder to overthrow Phocas. The
Exarchate of Africa now was created under Maurice in the 590s as a semi-autonomous
province under the control of an exarch, a governor with both civil and military authority.
Heraclius the Elder, another general of Maurice was thus the first Exarch of Africa based in
Carthage and after receiving letters from Priscus about the brutality and incompetence of
Phocas, he and his son Heraclius the Younger rebelled by proclaiming themselves consuls
in 608 and even minting coins with their faces.

Byzantine North Africa apparently was not the only area to rebel against Phocas’
rule as Syria and Palestine did the same too. In 609, Heraclius the Elder sent his nephew
Nicetas with an army to attack Egypt in order to block the grain shipments to
Constantinople as a move against Phocas. Despite Phocas sending troops to quell the
revolts in Egypt, they were defeated by Nicetas’ forces as they attacked Alexandria.

In the
meantime, the exarch’s son Heraclius the younger set sail from Carthage to Constantinople
arriving there in October of 610 meeting little resistance from Phocas’ troops. As Heraclius
arrived at Constantinople’s harbor, Phocas was tricked and betrayed by the Excubitors or
imperial guard and brought to Heraclius’ ship. After a brief exchange of words, Heraclius
personally executed Phocas and had his body mutilated and burned at a forum in
Constantinople together with the bodies of Phocas’ general Bonosus and official Leontius.

Following Phocas’ execution, the 35-year-old Heraclius on the same day was
crowned emperor by the new Patriarch of Constantinople Sergius who also married
Heraclius to Fabia Eudokia. Heraclius’ father the Exarch of Africa soon enough died after
hearing of his son’s victory. In the meantime, Phocas’ brother the general Comentiolus who
had a sizeable army in Asia Minor refused to recognize Heraclius’ authority but was
eventually assassinated by one of his own officers possibly under Heraclius’ orders, thus
neutralizing another threat to Heraclius. However, the Persian threat in the east was still at
large as despite Phocas’ fall from power, Khosrow II refused peace offers from Heraclius
believing he now had the upper hand in the war.

The Persian Threat Intensifies

During the civil war between Phocas and Heraclius from 608-610, the Sassanid
Persians taking advantage of the situation conquered most of Mesopotamia including
Edessa in 610 while raiding to as far as Chalcedon across the Bosporus from
Constantinople. The city of Caesarea Mazaca in Cappadocia too had fallen to the Persian
army under General Shahin. Heraclius himself together with Priscus who had switched his
support from Phocas to Heraclius thus laid siege to Caesarea, however Priscus pretended to
be ill which led to Shahin escaping Priscus’ blockade and burning Caesarea.

Because of this
action, Priscus was recalled by Heraclius to Constantinople in 612 and removed from
military command. Priscus was then replaced by Philippicus, an old general of Maurice but
he too was ineffective in battle against the Persians and so Heraclius took it upon himself to
lead the armies, the first Roman emperor to do so since Theodosius I (r. 379-395).

Due to the weakness of the Byzantine army at this point, Khosrow II ordered his
troops under General Shahrbaraz to push into Byzantine Syria. In 613, Heraclius leading
the army himself attempted to stop the Persian invasion of Syria but was defeated by
Shahrbaraz outside Antioch. The Persians thus captured Antioch and deported its
population to Persia whereas the rest of Byzantine Syria had fallen too. The Persians thus
proceeded south to Palestine and in 614, after a 3-week siege, Shahrbaraz captured
Jerusalem with the assistance of the city’s Jewish population.

Thousands of Jerusalem’s
citizens were slain by the Persians with 35,000 survivors deported to Persia together with
the city’s patriarch Zacharias. Many of Jerusalem’s holy sites were looted and desecrated by
the Persians including the Church of the Holy Sepulcher where the relic of the True Cross
was captured and taken to the Sassanid capital Ctesiphon. This was thus a major blow to
the Byzantine Empire’s mostly Christian population and many of them blamed the Jews for
this.

By 618, Persian forces under Shahrbaraz proceeded south into Byzantine Egypt
wherein most of its population who were Monophysite Christians oppressed by the
Chalcedonian Christian rule of the Byzantines welcomed the Persian army. The Persians
then laid siege to Alexandria which was defended by Heraclius’ cousin Nicetas and after a
year, the city fell in 619 when a traitor revealed to the Persians a way into the city through
an unused canal. As the Persians stormed Alexandria, Nicetas fled to Cyprus never to be
heard from again. The fall of Egypt to the Sassanids was a heavy blow to the Byzantines,
especially from Constantinople which received its grain supply from Egypt. Because of this,
Heraclius had to abolish the free grain ration which had been in practice since Ancient
Roman times.

Meanwhile, the Persians penetrated deep into Asia Minor going as far as to
Chalcedon again in 615. At this point, Heraclius considered submitting to Khosrow II as a
vassal and despite the Persian general Shahin receiving the peace offer, it was not accepted
by Khosrow. In the following years, the situation for the Byzantines became so grim that
Heraclius even considered abandoning Constantinople and moving the capital to Carthage
where it was safer but was persuaded to not do so by Patriarch Sergius. By this point, the
Byzantine economy too was in shambles that Heraclius had to devalue the currency and
with the situation so desperate, he even minted the phrase “may God help the Romans” on
his coins. To make things even worse for the Byzantines, plague broke out in 619 all while
the Persians by 620 captured several Byzantine Aegean islands including Rhodes.

The Byzantine Counteroffensive

Despite the desperate situation the Byzantine Empire was in, Heraclius refused to
give up. He eventually decided to launch a daring counteroffensive against the Persians but
to do it, he needed funding. In order to achieve the funds needed, Heraclius had to cut the
pay for his officials in half, increase taxation, force loans from the nobility, and fine corrupt
officials. Furthermore, with the consent of Patriarch Sergius, Heraclius ordered the Church
to melt their precious metal objects including golden chalices and frames to mint coins.

According to some historians, Heraclius in this war inspired the idea of “Crusading” as he
motivated his troops to fight not just to regain territory but to defend their Christian faith.
Before deciding to lead the daring counteroffensive, Heraclius took some time to study the
battle tactics of the Persians while also reading the military manual of the late emperor
Maurice known as the Strategikon which had extensive information about battling the
Persians.

In April of 622, Heraclius set off from Constantinople with what was left of the
Byzantine army to confront the Persians. Left behind in charge of the city were Heraclius’
son and heir Heraclius Constantine, the patriarch Sergius, and the patrician Bonus. During
the summer, Heraclius personally trained his own troops for the attack against the Persians
and by autumn, they marched straight into Persian-held Cappadocia forcing Shahrbaraz
and his forces to retreat from Galatia to defend inner Persia from Heraclius’ advance. By
this point, Heraclius had scored his first victory in battle against the Persians commanded
by Shahrbaraz, which he did so by feigning a retreat. This Byzantine victory though was
short lived as Heraclius had to return to Constantinople which was close to being attacked
by the Avars who by this point had overrun most of the Byzantine Balkans.

Because Heraclius was occupied in the war against the Persians, he decided to settle
peace with the Avars by sending an envoy to their ruler saying that he will pay tribute to
them in exchange for the Avars retreating north across the Danube. The Avars’ ruler or
khagan agreed to a meeting with Heraclius in 623 in Thrace. However, this was a trap as
when Heraclius arrived, the khagan’s men ambushed him so that he could be captured and
ransomed. Heraclius though managed to escape the ambush despite being chased all the
way to Constantinople by the Avar horsemen. Nevertheless, Heraclius was still able to
conclude a truce with the Avars by paying them a tribute of 200,000 solidi while also
sending prominent citizens as hostages to the Avars.

With the Avar threat taken care of, Heraclius returned to campaigning against the
Persians in 624, this time with the aim to attack the Persian heartland in Iran itself through
Armenia. En route, the Byzantines recaptured Cappadocia from the Persians and from there
advanced into Armenia before reaching Ganzak where Heraclius with the assistance of
Arab tribes routed a Persian army led by Khosrow II himself. During this campaign,
Heraclius had the famous Persian Zoroastrian fire temple of Adur Gushnasp destroyed.

Following this, Heraclius and his troops spent the winter in Caucasian Albania (Azerbaijan)
only to later be surrounded by three Persian armies- one led by Shahrbaraz, one by Shahin,
and the other by Shahraplakan- sent by Khosrow II. Heraclius though exploited the jealousy
the Persian commanders had for each other and first confronted the armies of Shahin and
Shahraplakan routing them both. After his victory, Heraclius crossed the Araxes River
where after being pursued by Shahrbaraz’s forces launched a surprise attack on
Shahrbaraz’s camp where Shahrbaraz caught off guard barely escaped naked and alone
losing his harem, baggage, and men.

Later in 625, Heraclius returned west to campaigning in Mesopotamia recapturing
key fortresses there from the Persians. At this point, Heraclius once again confronted
Shahrbaraz and his army at a bridge over the Sarus River in Cilicia. Although the
Byzantines won this battle with Heraclius advancing past his troops by crossing the bridge,
the Persian army retreated in an orderly way and would next target Constantinople itself
whereas Heraclius returned to winter in Trebizond.

The Siege of Constantinople, 626

Realizing that the Byzantines had now been gaining the upper hand in the war,
Khosrow II in 626 decided that it was time to launch a surprise counteroffensive on the
Byzantines, and this meant launching an attack on Constantinople itself. Khosrow II thus
recruited two armies from all the able men left within Persia, sent Shahin to defend
Mesopotamia and Armenia from Heraclius’ attack on Iran, and then had Shahrbaraz with
his army march to Chalcedon across Constantinople. Khosrow II too coordinated an
alliance with the same Avar khagan who tried to capture Heraclius in 623 by having him
and his men including his Slav subjects attack Constantinople on the European side. The
Avars thus began the siege of Constantinople by cutting off its water supply.

As the Persian army stationed themselves in Chalcedon waiting for the Slavs to ferry
them across the strait through their small boats, the Avars attacked the land walls of
Constantinople. However, this siege would soon turn out to be a failure for the attackers
due to poor communication between the Avars and Slavs attacking the land walls and the
Persians across the strait due to the Byzantine navy’s control of the Bosporus. This thus
reduced the effectiveness of the siege as the Persians had more advanced siege weapons.
Constantinople meanwhile was bravely defended by only 12,000 men under the command
of the patrician Bonus and Patriarch Sergius despite the attacking Avars and their subjects
being more superior in number with over 80,000 men.

When hearing the news of his capital under attack, Heraclius split his army into
three parts. The first division under him was to attack the Persian heartland, the second
under his brother Theodore was to deal with Shahin in Mesopotamia, and the third and
smallest one sent to reinforce Constantinople. Back in the capital, the Avars’ siege of the
land walls went on for an entire month though the morale of the defenders were high
thanks to Patriarch Sergius rallying the troops with religious processions. Furthermore, the
arrival of the Byzantine fleet at the Bosporus prevented the Persian troops from crossing it
through the Slavs’ boats which the larger Byzantine ships destroyed.

By August of 626, news had reached the Persians attacking Constantinople that
Heraclius’ brother Theodore had just defeated the Persians under Shahin in battle with
Shahin killed too. Because of this combined with their inability to cross the Bosporus, the
Persians under Shahrbaraz abandoned their plans to besiege Constantinople and retreated.
The Avars too abandoned their siege when hearing that the Persians had abandoned it too
and thus, they retreated north across the Danube never to threaten the Byzantines again.

The Byzantines here attributed their victory in the siege of 626 to the intervention of the
Virgin Mary and thus the Akathist Hymn was written due to this.

The Turn of the Tide

Because of the failure to take Constantinople, Khosrow II sent a letter to
Shahrbaraz’s second-in-command to execute Shahrbaraz and take command of his troops.
This letter though was intercepted by Byzantine troops who sent it to Heraclius’ son
Heraclius Constantine who in turn sent it to his father who then had it shown to
Shahrbaraz. When seeing it, Shahrbaraz had the letter altered claiming that Khosrow
intended to execute 400 officers and because of this, Shahrbaraz declared rebellion against
Khosrow switching to Heraclius’ side. Khosrow II was thus deprived of his most powerful
army and skilled general, therefore giving Heraclius more of an opportunity to win the war.
Shahrbaraz thus marched his army into Syria wherein he stayed neutral all while Heraclius
continued his advance into Persia.

Heraclius in the meantime had already formed an alliance with the nomadic Gok
Turks, the northern neighbor of the Sassanids who occupied most of Central Asia and
Southern Russia. The Gok Turk Khaganate apparently had already been a common ally of
the Byzantines against the Sassanids ever since the reign of Byzantine emperor Justin II in
the 560s. In 626 though, Heraclius reconfirmed this alliance with the Gok Turks by offering
lavish gifts and his daughter Eudoxia Epiphania in marriage to their ruler Tong Yabghu, also
known in Byzantine sources as Ziebel.

The Gok Turks thus invaded Sassanid territory
through the Caucasus wherein they joined the Byzantines in besieging Tiflis (Tbilisi) which
was held by the Sassanid Persian-allied Iberians. With the use of traction trebuchets for the
first time recorded, the city had fallen. The Byzantines however abandoned the siege of
Tiflis leaving the job of finishing it to the Gok Turks as they were now to strike into the
Persian heartland.

In 627, Heraclius led his army straight into the Persian heartland tailing the last
Persian army under the command of General Rhahzadh. In December of 627, Heraclius
confronted the last Persian army at the Battle of Nineveh wherein the Persians were at a
disadvantage due to the fog. Heraclius here managed to score a decisive victory by once
again feigning a retreat and crashing into the confused Persians. At the end, it was said that
over 6,000 Persian soldiers had died in battle whereas the 9th century Byzantine historian

Patriarch Nikephoros claimed that Heraclius personally challenged Rhahzadh in a duel
killing him and two other commanders whereas Heraclius only received a wound in his lip.

After his victory at the Battle of Nineveh, Heraclius proceeded to attack several of
Khosrow II’s palaces including Dastagird wherein they discovered so much riches including
silk, spices, and over 300 Roman and Byzantine battle standards the Persians captured over
the centuries which Heraclius had much of them burned as it was too much for his army to
carry back home. The Byzantines though were unable to take the Persian capital Ctesiphon
as the Persians had cut off all bridges leading to it to prevent an attack. Heraclius
meanwhile issued an ultimatum to Khosrow to accept peace terms, though Khosrow still
refused.

Due to his recent defeats against the Byzantines, by early 628, Khosrow II had lost
the support of his nobility and army who then raised his son Siroy as the new Sassanid
shah Kavad II against him. Khosrow was thus imprisoned and then shot to death multiple
times by arrows. The new shah Kavad II immediately sued for peace with Heraclius who in
turn did not demand harsh terms. As part of the terms of this peace treaty, the Persians
were to return all territory they captured since the beginning of the war back to the
Byzantines, return captured soldiers, and most importantly return the relic of the True
Cross which the Persians captured from Jerusalem in 614.

The Aftermath

Although the great war had ended in early 628, it took several months for the
Persian troops to fully retreat from Byzantine territory which the Byzantines had just taken
back as part of the treaty with Kavad II. After months of touring the empire and restoring
order to the newly regained provinces, Heraclius finally returned to Constantinople in 629
with an elaborate triumphal parade. Here, the recovered True Cross was placed in
Constantinople’s main cathedral, the Hagia Sophia for all to see. However, the Cross did not
remain there for long as in 630, Heraclius returned it to Jerusalem, its rightful place.

As for the Sassanid Empire, their defeat in the war created internal instability and
civil war which followed the death of Kavad II later in 628. In 630, Shahrbaraz with the
support of Heraclius put his claim on the Sassanid throne and briefly ruled after taking

Ctesiphon and killing Kavad II’s son and successor Ardashir III. Shahrbaraz though was
killed by his rivals after ruling for only a month all while the Sassanid civil war would
continue until 632 with the accession of Khosrow II’s grandson Yazdegerd III, but by then
the Sassanid Empire had been already severely exhausted.

Despite the Byzantines’ ultimate victory in the war against the Sassanid Persians in
628, their empire had been greatly exhausted both militarily and economically. Just less
than a decade later, the Byzantines would face a new rising enemy from the south, the
Arabs now having united as the Rashidun Caliphate under the new faith of Islam in which
the Byzantines no longer had the resources to stand up against.

Before Heraclius’ death in
641, the Byzantines once again suffered major defeats losing almost everything they
regained from the Persians in the Middle East including Egypt to the new power of the
Arabs. Although the Byzantine Empire survived and was able to defend against the Arab
expansion which began in the 630s, their empire was forever reduced in territory. The
Sassanid Empire meanwhile further weakened by their defeat in the war against the
Byzantines stood no chance against the Arab expansion and thus by the 650s, they ceased
to exist.