Emperor Heracluis

Learning Objective

  • Identify the reason for the reduction in size of the Byzantine Empire

Key Points

  • After Justinian, the Byzantine Empire continued to lose land to the Persians.
  • Emperor Heraclius seized the throne in 610 CE, and beat back the Persians by 628 CE.
  • However, after Heraclius’ victory against the Persians, he had taken such losses that he was unable to defend the empire against the Arabs, and so they again lost the lands they had just reconquered by 641 CE.
  • Heraclius tried to unite all of the various religious factions within the empire with a new formula that was more inclusive and more elastic, called monothelitism, which was eventually deemed heretical by all factions.



The central figure of Islam, widely regarded as its founder.


The view that Jesus Christ has two natures but only one will, a doctrine developed during Heraclius’ rule to bring unity to the Church.

Conflict with the Persians and Chaos in the Empire

Ever since the fall of the Western Roman Empire, the Eastern Roman Empire had continued to see western Europe as rightfully Imperial territory. However, only Justinian I attempted to enforce this claim with military might. Temporary success in the west was achieved at the cost of Persian dominance in the east, where the Byzantines were forced to pay tribute to avert war.

However, after Justinian’s death, much of newly recovered Italy fell to the Lombards, and the Visigoths soon reduced the imperial holdings in Spain. At the same time, wars with the Persian Empire brought no conclusive victory. In 591 however, the long war was ended with a treaty favorable to Byzantium, which gained Armenia. Thus, after the death of Justinian’s successor, Tiberius II, Maurice sought to restore the prestige of the Empire.

Even though the empire had gained smaller successes over the Slavs and Avars in pitched battles across the Danube, both enthusiasm for the army and faith in the government had lessened considerably. Unrest had reared its head in Byzantine cities as social and religious differences manifested themselves into Blue and Green factions that fought each other in the streets. The final blow to the government was a decision to cut the pay of its army in response to financial strains. The combined effect of an army revolt led by a junior officer named Phocas and major uprisings by the Greens and Blues forced Maurice to abdicate. The Senate approved Phocas as the new emperor, and Maurice, the last emperor of the Justinian Dynasty, was murdered along with his four sons.

The Persian King Khosrau II responded by launching an assault on the empire, ostensibly to avenge Maurice, who had earlier helped him to regain his throne. Phocas was already alienating his supporters with his repressive rule (introducing torture on a large scale), and the Persians were able to capture Syria and Mesopotamia by 607.

While the Persians were making headway in their conquest of the eastern provinces, Phocas chose to divide his subjects, rather than unite them against the threat of the Persians. Perhaps seeing his defeats as divine retribution, Phocas initiated a savage and bloody campaign to forcibly convert the Jews to Christianity. Persecutions and alienation of the Jews, a frontline people in the war against the Persians helped drive them into aiding the Persian conquerors. As Jews and Christians began tearing each other apart, some fled the butchery into Persian territory. Meanwhile, it appears that the disasters befalling the empire led the emperor into a state of paranoia.

The Heraclian Dynasty Under Heraclius

Due to the overwhelming crises that had pitched the empire into chaos, Heraclius the Younger now attempted to seize power from Phocas in an effort to better Byzantium’s fortunes. As the empire was led into anarchy, the Exarchate of Carthage remained relatively out of reach of Persian conquest. Far from the incompetent Imperial authority of the time, Heraclius, the Exarch of Carthage, with his brother Gregorius, began building up his forces to assault Constantinople. In 608, after cutting off the grain supply to the capital from his territory, Heraclius led a substantial army and a fleet to restore order in the Empire. The reign of Phocas officially ended in his execution, and the crowning of Heraclius by the Patriarch of Constantinople two days later on October 5, 610. After marrying his wife in an elaborate ceremony and being crowned by the Patriarch, the 36-year-old Heraclius set out to perform his work as emperor. The early portion of his reign yielded results reminiscent of Phocas’ reign, with respect to trouble in the Balkans.

To recover from a seemingly endless string of defeats, Heraclius drew up a reconstruction plan of the military, financing it by fining those accused of corruption, increasing taxes, and debasing the currency to pay more soldiers and forced loans.

Instead of facing the waves of invading Persians, he went around them, sailing over the Black Sea and regrouping in Armenia, where he found many Christian allies. From there, he invaded the Persian Empire. By fighting behind enemy lines, he caused the Persians to retreat from Byzantine lands. He defeated every Persian army sent against him and then threatened the Persian capital. In a panic, the Persians killed their king and replaced him with a new ruler who was willing to negotiate with the Byzantines. In 628 CE, the war ended with Heraclius’ defeat of the Persians.


Emperor Heraclius. A plaque depicting Byzantine Emperor Heraclius overcoming Persian King Khosrau II, c. 1160-1170 CE.

The Arab Invasion

By this time, it was generally expected by the Byzantine populace that the emperor would lead Byzantium into a new age of glory. However, all of Heraclius’ achievements would come to naught, when, in 633, the Byzantine-Arab Wars began.

On June 8, 632, the Islamic Prophet Muhammad died of a fever. However, the religion he left behind would transform the Middle East. In 633, the armies of Islam marched out of Arabia with a goal to spread the word of the prophet, with force if needed. In 634, the Arabs defeated a Byzantine force sent into Syria and captured Damascus. The arrival of another large Byzantine army outside Antioch (some 80,000 troops) forced the Arabs to retreat. The Byzantines advanced in May 636. However, a sandstorm blew in against the Byzantines on August 20, 636, and when the Arabs charged against them, they were utterly annihilated.

Jerusalem surrendered to the Arabs in 637, following a stout resistance; in 638, the Caliph Omar rode into the city. Heraclius stopped by Jerusalem to recover the True Cross whilst it was under siege. The Arab invasions are seen by some historians as the start of the decline of the Byzantine Empire. Only parts of Syria and Cilicia would be recovered.

Religious Controversy

The recovery of the eastern areas of the Roman Empire from the Persians during the early phase of  Heraclius’ rule raised the problem of religious unity centering on the understanding of the true nature of Christ. Most of the inhabitants of these provinces were Monophysites who rejected the Council of Chalcedon of 451. The Chalcedonian Definition of Christ as being of two natures, divine and temporal, maintains that these two states remain distinct within the person of Christ and yet  come together within his one true substance. This position was opposed by the Monophysites, who held that Christ possessed one nature only; the human and divine natures of Christ were fused into one new single (mono) nature. This internal division was dangerous for the Byzantine Empire, which was under constant threat from external enemies, many of whom were in favor of Monophysitism, people on the periphery of the Empire who also considered the religious hierarchy at Constantinople to be heretical and only interested in crushing their faith.

Heraclius tried to unite all of the various factions within the empire with a new formula that was more inclusive and more elastic. With the successful conclusion to the Persian War, Heraclius would devote more time to promoting his compromise.

The patriarch Sergius came up with a formula, which Heraclius released as the Ecthesis in 638. It forbade all mention of Christ possessing one or two energies, that is, one or two wills; instead, it now proclaimed that Christ, while possessing two natures, had but a single will. This approach seemed to be an acceptable compromise, and it secured widespread support throughout the east. The two remaining patriarchs in the east also gave their approval to the doctrine, now referred to as Monothelitism, and so it looked as if Heraclius would finally heal the divisions in the imperial church.

Unfortunately, he had not counted on the popes at Rome. During that same year of 638, Pope Honorius I had died. His successor, Pope Severinus (640), condemned the Ecthesis outright, and so was forbidden his seat until 640. His successor, Pope John IV (640-42), also rejected the doctrine completely, leading to a major schism between the eastern and western halves of the Chalcedonian Church. When news reached Heraclius of the pope’s condemnation, he was already old and ill, and the news only hastened his death, declaring with his dying breath that the controversy was all due to Sergius, and that the patriarch had pressured him to give his unwilling approval to the Ecthesis.