Byzantine Empire under the Heraclian dynasty The Byzantine Empire was ruled by emperors of the dynasty of Heraclius between 610 and 711 . The Heraclians presided over a period of cataclysmic events that were a watershed in the history of the Empire and the world in general . At the beginning of the dynasty , the Empire was still recognizable as the Eastern Roman Empire , dominating the Mediterranean and harbouring a prosperous Late Antiquity urban civilization . This world was shattered by successive invasions , which resulted in extensive territorial losses , financial collapse and plagues that depopulated the cities , while religious controversies and rebellions further weakened the Empire . By the dynasty ' s end , a very different state had emerged : medieval Byzantium , a chiefly agrarian , military - dominated society that was engaged in a lengthy struggle with the Muslim Caliphate . However , this state was also far more homogeneous , being reduced to its mostly Greek - speaking and firmly Chalcedonian core territories , which enabled it to weather these storms and enter a period of stability under the successor Isaurian Dynasty . The Heraclian dynasty was named after the general Heraclius the Younger , who , in 610 , sailed from Carthage , overthrew the usurper Phocas , and was crowned Emperor . At the time , the Empire was embroiled in a war with the Sassanid Persian Empire , which in the next decade conquered the Empire ' s eastern provinces . After a long and exhausting struggle , Heraclius managed to defeat the Persians and restore the Empire , only to lose these provinces again shortly after to the sudden eruption of the Muslim conquests . His successors struggled to contain the Arab tide . The Levant and North Africa were lost , while in 674 – 678 , a large Arab army besieged Constantinople itself . Nevertheless , the state survived and the establishment of the Theme system allowed the imperial heartland of Asia Minor to be retained . Under Justinian II and Tiberios III the imperial frontier in the East was stabilized , although incursions continued on both sides . The latter 7th century also saw the first conflicts with the Bulgars and the establishment of a Bulgarian state in formerly Byzantine lands south of the Danube , which would be the Empire ' s chief antagonist in the West until the 11th century . Background . Ever since the fall of the Western Roman Empire , the Eastern Roman Empire 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 . By 608 , the Persians were camped outside Chalcedon , within sight of the imperial capital of Constantinople , while Anatolia was ravaged by Persian raids . Making matters worse was the advance of the Avars and Slavic tribes heading south across the Danube and into Imperial territory . 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 drove 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 — although it must be said that there were numerous plots against his rule and execution followed execution . Among those individuals who were executed was the former Constantina and her three daughters . Heraclius . Phocas deposed by Heraclius the Younger . Due to the overwhelming crisis facing the Empire that had pitched it 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 . After cutting of the grain supply to the capital from his territory , Heraclius led a substantial army and a fleet in 608 to restore order in the Empire . Heraclius gave the command of the army to Gregorius ' son , Nicetas , whilst command of the fleet went to Heraclius ' son , Heraclius the Younger . Nicetas took part of the fleet and his forces to Egypt , seizing Alexandria towards the end of 608 . Meanwhile , Heraclius the Younger headed to Thessalonica , from where , after receiving more supplies and troops , he sailed for Constantinople . He reached his destination on 3 October 610 , where he was unopposed as he landed off the shores of Constantinople , citizens greeting him as their deliverer . When Phocas was delivered to Heraclius , an interesting conversation took place : The reign of Phocas officially ended in his execution and the crowning of Heraclius by the Patriarch of Constantinople two days later on 5 October . A statue of Phocas that rested in the Hippodrome was pulled down and set aflame , along with the colors of the Blues that supported Phocas . Early failures . After having married his wife in an elaborate ceremony and 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 . The Avars and Slavs poured through the western Adriatic , as well as through the southern and eastern portions of the Aegean area . Their sweeping movement into Dalmatia engulfed several Byzantine cities , namely Singidunum ( Belgrade ) , Viminacium ( Kostolac ) , Naissus ( Niš ) , Sardica ( Sofia ) , and destroyed Salona in 614 . However , numerous attempts to take the city of Thessalonica by the Slavs and Avars ended in failure , allowing the Empire to hold onto a vital city in the region . In 613 , the Byzantine army suffered a crushing defeat in Antioch , allowing the Persians to move freely and swiftly in all directions . This surge caused the cities of Damascus and Tarsus to fall , along with Armenia . More seriously , however , was the loss of Jerusalem , which was besieged and captured by the Persians in three weeks . Countless churches in the city ( including the Holy Sepulchre ) were burnt and numerous relics , including the True Cross , the Holy Lance and the Holy Sponge , present at the time of Jesus Christ ' s death , were now in Ctesiphon , the Persian capital . The Persians remained poised outside of Chalcedon , not too far from the capital , and the province of Syria was in total chaos . Despite Nicetas ' earlier efforts , Egypt was also conquered , resulting in a significant loss in manpower , food supplies and revenue . However , the situation was not entirely hopeless . Constantinople ' s walls were as powerful and well - defended as ever , and Heraclius still had a large , better - trained , and better - armed fleet than any of his " barbarian " opponents ( especially the Slavs and Avars ) . The Persians had no vessels in the Bosporus , and thus unable to effectively besiege the city . Byzantine counter offensive . To recover from a seemingly endless amount of defeats , Heraclius went about 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 . The Patriarch of Constantinople , Sergius , placed the finances of the Church into the hands of the State , a surprising but well - needed sacrifice . Heraclius now aimed to eliminate one of his dangerous foes , the Sassanid Empire . The Persians had conquered extensive amounts of territory in Anatolia , Mesopotamia , the Levant , and North Africa , but had yet to consolidate their hold on it . Heraclius decided to negotiate a peace with the Avars and Slavs by paying them a large amount of tribute so that he could freely move his armies from Europe to Asia in order to launch counter - offensives against the Persians . With his Eastern opponents still outside Chalcedon , in the spring of 622 Heraclius took the field . He sailed his newly created army down the Ionian coast and landed at Issus , the exact site where Alexander the Great had decisively defeated the Persians some 1 , 000 years prior . At Issus , Heraclius oversaw the extensive training of his men . In the autumn of that year , he marched his army northwards and encountered a Persian force in the Cappadocian highlands . Despite having no military experience in leading an army in the field , the Byzantine Emperor decisively routed the forces of the experienced Persian General Shahrbaraz , boosting his army ' s morale and recovering large amounts of territory . In early 623 , Heraclius led his forces through Armenia and modern - day Azerbaijan . By moving towards Armenia , this forced the Persians to move from their positions in Asia Minor and to follow the army " like a dog on a chain " . It was in Armenia that the Byzantine army once again found success against the Persian general Shahrbaraz , winning a large victory . Events in the capital forced Heraclius and his army to return to Constantinople , as the Avar Khan was threatening action on the city . Heraclius was forced to increase the tribute being paid to the Avars , even having to go as far as sending hostages to the Khan to ensure payment . This once again shored up his rearguard , allowing him to re - engage the Persian army in March 623 , as the Persian king Chosroes II had become ever more belligerent in his attitude , spurning a truce . On the way to Persia , the Byzantine army pillaged and looted extensively , including the destruction of the Persian palace at Ganzak . Burning numerous cities of his opponents , Heraclius made a risky decision and led his troops deep within the heartland of the Sassanid Empire to Ctesiphon , the Persian capital . However , Shahrbaraz began cutting off Heraclius ' supply lines , forcing the latter to withdraw to the western shore of the Caspian Sea . There , his second wife and niece ( Martina ) safely delivered a child , although the marriage was seen by many as incestuous . In 624 , Heraclius led another campaign towards Lake Van . However , the victory that he sought would not come to him until the following year . Leading his army through Ararat down the Arsanias River for some to capture the cities of Martyropolis and Amida , Heraclius finally encountered a Persian army north of the town of Adana after marching through Mesopotamia . Initially , the battle went well for the Persians , as they obliterated the vanguard of the Byzantine army . However , Heraclius then seized the initiative by launching a seemingly suicidal charge across the River Euphrates , thus turning the tide of the battle . Even Shahrbaraz did not deny the bravery of the Emperor : Siege of Constantinople . Victory belonged to the Byzantines , and now , the honours of the war were even . However , the Persian threat was not yet diminished . The long - awaited assault on Constantinople was finally beginning to materialize — the Avars began moving siege equipment towards the Capital ( the siege began on June 29 , 626 ) whilst Shahrbaraz was ordered by King Khosrau II to send his army to Chalcedon and link up with the Avars . Khosrau began conscripting able - bodied men into a new army , raising a crack force of approximately 50 , 000 men . Heraclius , it seems , was not only being outmaneuvered , but being outmaneuvered by several larger armies . However , Heraclius attempted to match the Persians by duplicating their strategy and dividing his forces into three separate contingents . One army would defend the capital , whilst another , under the command of the Emperor ' s brother Theodore , would face the 50 , 000 conscripts in Mesopotamia who were commanded by the Persian General Shahin . Meanwhile , the third , which would be personally commanded by the Emperor , would march through Armenia and the Caucasus and into Persia , which he believed would have been stripped of most of the able - bodied men due to Khosrau ' s conscription . This would allow his forces to easily advance into the heartland of Persia . Theodore ' s contingent fared well against Shahin in Mesopotamia , inflicting a crushing defeat on the Persians . During this battle , at Constantinople , the city was well defended with a force of some 12 , 000 cavalry ( presumably dismounted ) , supported by the entire city ' s population . Indeed , the efforts of the Patriarch Sergius in whipping up the population into a religious and patriotic frenzy cannot be overlooked . When the Byzantine fleet annihilated a Persian and an Avar fleet in two separate ambushes , the besiegers appeared to have withdrawn in panic . And when word of Theodore ' s victory in Mesopotamia came , it was concluded by the besiegers that Byzantium was now under the protection of the Romans ' Christian God . Endgame . For Heraclius , 626 was a year of little action — it appears that in an attempt to bolster his forces , he promised the hand of his daughter Epiphania to the Khan of the Western Turkic Khaganate , Ziebel . Impressed by the offer ( though no doubt Epiphania was not ) , the Khan fielded some 40 , 000 troops on the Byzantine side . It would be to Epiphania ' s great relief that the Khan died just two years later , in 628 . Nonetheless , Byzantium made good use of the boost in troops when Heraclius marched into Mesopotamia the following year . His objective was clear : to destroy the Persians ' army and march to Ctesiphon , doing what no Roman Emperor had done in nearly three - hundred years ( since the days of Julian the Apostate ) : . His army marched cautiously into this hostile terrain . It was known to Heraclius that a Persian force was close and an ambush was always a possibility . Meanwhile , Rhahzadh , the new Persian commander , was also not keen to face Heraclius until his army was ready for a pitched battle . After spending a greater part of 627 in Mesopotamia , Heraclius finally encountered the Persian army close to the ruins of the city of Ninevah . For eleven hours , the Byzantines and the Persians fought each other continuously . In the thick of the fighting Razates issued a challenge to Heraclius , who accepted . Despite being wounded , Heraclius managed to decapitate Razates . When the sun finally began to set , the Persians had been defeated and both armies rested . Heraclius later moved on to the Great Palace of Dastagird only to discover that Khosrau II had fled his Palace . In a fit of rage , Heraclius ordered that everything be burnt to the ground . Moving on , he soon found that Khosrau no longer commanded the loyalty of his subjects — as they refused to rally to defend Ctesiphon . Heraclius waited a week or two before marching his army back . Khosrau ' s son Siroes took power as Kavadh II and had his father shot to death with arrows . Later , the formation of a peace treaty favourable to the Byzantines led to the restoration of the pre - war boundaries . As an added bonus , all captives and Christian relics that had been captured by the Persians were returned . Thus , it was at the head of the True Cross that Heraclius entered the Capital on September 14 , 628 triumphant . Leading a procession which included four elephants , the True Cross was placed high atop the altar of the Hagia Sophia . 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 . Decline . The threat of the Arabs from Arabia was overlooked by both Persia and Byzantium for several reasons — most compelling of all were the wars between the two powers , and the lack of communication across the desert expanse . Nonetheless , efforts were conducted , sometimes cooperatively , by the Byzantines and the Persians to stop the advance of the Arabs . On 8 June 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 , their 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 on 20 August 636 against the Byzantines 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 . In his old age he was becoming increasingly unstable in his rule . Once the commander of his father ' s fleet , he developed a phobia of the sea , and refused to cross the Bosporus to the capital . Only when several boats were tied along the length of the strait with shrubs placed along to hide the water did he ride across , " as if by land " as a contemporary put it . The Arab invasions and loss of territory was not all that bore heavily upon the Emperor ' s mind . It was rumoured that the incestuous marriage to his niece had incurred the wrath of God — of the nine children that he had , four had died in infancy , one had a twisted neck and one was deaf and dumb . Furthermore , it appears that the Empire was not even considering the Arab threat as a danger . The religious controversies once again emerged when the Patriarch of Constantinople Sergius proposed monothelitism as a compromise to the Chalcedonian Christians and the Monophysite s . Heraclius agreed to the proposal . However , it received much criticism from both sides of the theological debate of Christ ' s true nature . When Sophronius , a major critic of monothelitism was elected as Patriarch of Jerusalem , the Empire began once again to tear itself apart . To some in the Empire the Arabs ' promise of religious freedom seemed preferable to the other , seemingly blasphemous politically motivated proposals . At his death bed on 11 February 641 , Heraclius died whispering that he had lied ; he was reluctant to support monothelitism . It appears that unity was all that he sought . Before his death Heraclius was " persuaded " by his wife Martina to crown her son Heraclonas ( " Flavius Heraclius " ) co - heir to the throne of the Empire with Constantine , the son of Heraclius ' first wife Eudocia — all the meanwhile ignoring the numerous Byzantines who saw her as the reason for Byzantium ' s recent misfortunes . Her ambitions for power ensured that Byzantium would continue to succumb to disorder . Heraclius ' rule . Early on , Heraclius had proven himself to be an excellent Emperor — his reorganization of the Empire into Themes allowed the Byzantines to extract as much as they possibly could to increase their military potential . This became essential after 650 , when the Islamic Caliphate was far more resourceful and powerful then the Byzantines were . As a result a high level of efficiency was needed to combat the Arabs , achieved in part due to the Theme system . Heraclius also completed the Hellenization of the Empire by making Greek the language of the Empire – Latin became a language increasingly for the upper class . As the Empire lost her outer lands , the number of Greek speakers rose and Latin was no longer advantageous to use . Heraclius abandoned the words " Imperator " , " Augustus " and other Imperial titles in favor of the word " Basileus " , the Greek word for " King " . It is perhaps this transformation that results in coins bearing the motto , " King over Kings , Ruler of Rulers " , a defunct saying for post - 640 Byzantium , considering what little land was left under Imperial rule . Had Heraclius lived only until 629 , he would have been remembered for his Themes and his astonishing handling of the last Persian war , which saw victory snatched from the jaws of defeat . However , his lengthy life meant that the Byzantines remembered him for his religious controversies , his failures against the Arabs and the incestuous marriage to his niece , which many believed to have brought divine retribution upon the entire Empire . After his death , Heraclius ' corpse remained unburied for three days , guarded by his soldiers until it was laid to rest in the Church of the Holy Apostles within a sarcophagus of white onyx next to the founder of his Empire , Constantine I . The Theme system . The army of the Empire that Heraclius worked so hard to improve eventually was reorganized in Asia Minor into four " Themes " , in what is now known as the Theme system . This system was originally credited by Byzantine historians like George Ostrogorsky to Heraclius . He provides Theophanes as a source , quoting the expression " the district of the themes " in the year 622 , showing the themes had begun to be created at this time . However , there is evidence presented by some modern historians that it could possibly be credited to Constans , and yet others leave the door open that Heraclius could possibly have done so in the late 630s in Cilicia . In any case , the debate over exactly when the thematic system originated continues on . The administrative regions created from this system were to be governed by a " strategos " , a military governor . The aim of these Themes was to maximize military potential — many able - bodied men and their families were settled in these four themes and given land for farming . In return for land , these men were to provide the Empire with loyal soldiers , and so began the Thematic armies of the Byzantine Empire that would prove to be reliable , though not unbeatable fighting force for centuries to come . Nonetheless , a native , well - trained army loyal to the state would serve the Empire far more than ill - disciplined mercenaries , whose loyalty to coin could be manipulated and turned against the state itself , as had been exemplified during the Fall of the Western Roman Empire . Constans II . Death of Heraclius . Heraclius ' inability to rule the Empire as his death neared did Byzantium no favors . After Heraclius ' death in 641 , the former Empress Martina declared herself , her son , Heracleonas , and her stepson , Constantine , co - emperors of the Byzantine Empire . However , the citizens of Constantinople refused to accept this . And so , when Constantine III died sometime between May 24 and May 26 , 641 ( considered by the majority of the Byzantines to have been done by Martina ' s hand ) , Heracleonas and his mother were deposed the following summer . Heraclonas ' nose was slit and Martina ' s tongue was wrenched out . These acts ensured that Heraclonas could never become " Basileus " ( Emperor ) – the physical deformation would have made it impossible . However , as suspects of committing regicide , their exile to the island of Rhodes was a been a light punishment . With Constantine dead , the populace of Constantinople turned to his 11 - year - old son ( also known as Heraclius ) who was crowned as the Byzantine Emperor , and changed his name to Constans , thus becoming Constans II . Wars with the Arabs . Constans II had inherited from his grandfather Heraclius the war with the Arabs , who were bent on conquering the Byzantine Empire and spreading the word of the Islamic Prophet Muhammad . Upon his ascension , there was little time to implement a defence for Egypt — and when the province fell in 642 , Constans II could hardly be blamed . The loss of Egypt and the Levant was catastrophic — along with the manpower from these regions , the substantial supply of food from Egypt was now but a thing of the past . Food shortages were now added to an increasing list of problems that the Emperor was facing . And to make matters worse for the Byzantines , the Arab armies gave no respite — by 647 the Exarchate of Carthage had been decisively defeated — another costly defeat as Africa was the Empire ' s main source of grain , aside from already lost Egypt . The list of defeats would continue to grow , as in 644 , the Arabs began building a sizable fleet to take on the centuries of Greco - Roman naval dominance . In 657 , the Arab fleet was sent to raid the Byzantine island of Cyprus — the island was barely defended , and the Arabs sacked the chief city of Constantia destroyed its harbor installations and ravaged the countryside . In 654 , the Muslim fleet continued unopposed to the island of Rhodes . After the island fell , Constans II suffered another humiliating defeat at the Battle of the Masts , when he sent his fleet to engage the Arabs off Lycia . During the engagement , Constans II , fearing the possibility of being captured , exchanged clothing with another man so that he could escape without being identified . Though never captured , the experience was rather embarrassing for the so - called " King of Kings " . Respite . By this point , the Arabs appeared to the Romans as invincible , and thus , could only hinder themselves . Fortunately for Byzantium , the Arabs began to do just that . The Caliph Uthman ibn Affan was assassinated in Medina . As a result , Ali , the Islamic Prophet Muhammed ' s son - in law was elected as his successor . However , Muawiya , the governor of Syria who led the Arab fleet against Byzantium , was proclaimed Caliph in Syria , as well . Only when Ali was assassinated in 661 did the civil strife end , much to Byzantium ' s disappointment . Attempts to deal with religious controversies . Clearly , Byzantium stood no chance whatsoever of defending herself against her opponents when bishops tore the Empire over theological debates . Constans II saw this and it seems that he had enough of it . In 648 , Constans still only 18 years of age , declared an edict that no one would raise the monethelism / chalcedon controversy under the pain of banishment , following an excommunication by the Pope Theodore I to the Patriarch of Constantinople Pyrrhus . When Theodore ' s successor , Martin I once again added fuel to the fire by summoning a council in condemnation of Monethelitism in October 648 , he was arrested , brought to the capital and badly mistreated as a common criminal . In prison it is said the his mistreatment was " such that blood was on the floor . " Finally , after being accused of treason and regicide he was banished to the Crimea . Such was the frustration of the Emperor . To the West . Constans II decided to turn his attention to the West in the hope of achieving better luck . Whilst the Saracens were establishing themselves in former Byzantine territory , the Avars and Bulgars still remained along the Danube river , as did the Slavs , whose annual payment to the Empire was falling short . Constans II then decided to move his capital to Syracuse in Sicily in 662 . Some say that this was to escape horrible visions of his brother whom he had murdered 2 years past . His stay in Italy and Sicily can only be imagined as unpleasant for the locals . Everything of any value in Rome was requisitioned by the Byzantine army — even copper from the rooftops . It was to many people ' s relief that Constans II was murdered while bathing by his Greek servant on 15 September 668 . Constans II left the Empire in a worse state than he had found it . The Byzantine - Arab wars became increasingly one - sided and the immense resources of the Caliphate meant that any reconquest was now remotely unlikely — and more so whilst disunity through dissatisfied peasants and restless Bishops lingered on . Constantine IV . Constantine IV would prove to be a much wiser and able Emperor than Constans II was . Siege of Constantinople . Like his predecessors , the wars with the Saracens continued relatively unabated . Before becoming Emperor , Constantine IV was the administrator of his father ' s lands for the eastern portions of the Empire , what few territories they were . They became fewer still when the Arabs began taking one Imperial Byzantine city after another along the coast of Ionia . Finally in 672 , Muawiya the Caliph captured the peninsula of Cyzicus , only from Constantinople . The scene was all too depressingly familiar — the capital was under threat and the odds were not favorable to the defenders — the Arabs had brought with them heavy siege weapons and began the siege of Constantinople in 674 . Despite this , Constantinople was simply too much for the Arabs — where else before disunity , sheer bad luck or skill & zeal had given the warriors of Islam victory , now it was the defenders of the capital who , armed with Greek fire repelled every Arab assault . Finally in 678 , after suffering massive casualties , the Saracens withdrew and Muawiya accepted an offer of peace . By 680 , Muawiya was dead and Constantine IV , now at the height of his popularity , had managed to defeat the Arabs , both at land in Lycia and at sea . Wars with the Bulgars . With the Saracen threat averted , the Byzantines turned their attention to the west , where the Bulgars were encroaching on Imperial territory . In 680 , Constantine IV launched a naval expedition to drive them back — the expedition failed and the Bulgars grew even bolder . Unable to stop them by force , Constantine settled for a humiliating , but not disastrous treaty whereby " protection " money had to be paid to the Bulgar King . The greatest implication of this treaty was that Byzantium would no longer have to worry about the Bulgars for the rest of Constantine ' s reign . Third Council of Constantinople . Constantine IV was determined to solve the problem of the monotheletism / chalcedon controversy once and for all . Calling forth representatives from all corners of Christendom to discuss the matter at hand , they debated until in 681 when Constantine IV , who had presided over much of the meetings , endorsed the virtually unanimous findings . Four years later in 685 , Constantine IV died . His death at thirty three years robbed Byzantium of a good Emperor who had defeated her enemies from within as well as without . Constantine ' s wife Anastasia had given him a son , Justinian . As it would turn out , his name would dictate his foreign policy in an attempt to emulate Justinian I ' s conquest of the West — a risky move considering what few resources the Empire had to defend herself . Justinian II . Victories . The beginning of Justinian ' s reign continued the successes his father had enjoyed against the Arab invaders . Campaigning into Armenia , Georgia and even Syria , he was able to enforce a renewal of a peace treaty signed by his father and the Caliph . With the wars in the east favorably concluded , Justinian II turned his attention to the west where he sent an expedition against the Slavs between 688 and 689 . His success in the west was crowned with a triumphant entry into Thessalonika , the second city of the Empire . Following these victories , Justinian set about attempting to increase the Opsikion Theme by bringing in some 250 , 000 settlers of Slavic origin into Asia Minor . The benefit of the move was twofold — in addition to opening up more agricultural land , there would also have been an increase in the population and a larger number of Thematic militia troops could be raised — allowing the Empire to wage war with more . Furthermore , the increase in the lower classes shifted the balance of power from the aristocracy to the class of well - off peasants . These self - sufficient peasants , who owned their own land formed the backbone of the Thematic armies . Under such circumstances the power of the Empire and the Emperor increased simultaneously . Since pre - Imperial times the Plebeians looked towards a military champion to combat the rule of the aristocracy , thus the Plebs supported a strong emperor . Failures . In 691 , war with the Arabs resumed and Justinian began increasing taxes in order to finance the conflict . However , in the face of these extortionate requisitions some 20 , 000 Slavic soldiers deserted to the Arabs — with them went Armenia to the enemy . Enraged , Justinian ordered the extermination of all Slavs in Bithynia — countless men , women and children were put to the sword in rage . Justinian then turned his attention to religious matters , which had been quietended down by the efforts of his father . When he called another council to wrap up loose ends from the previous ( fifth and sixth - thus called Quinisext Council ) ecumenical council s , trivial and strict proposals were laid out including excommunication for " crimes " ranging from provocative or seductive hair curling , the mention of the pagan gods ( especially Bacchus during the grape harvest ) , the selling of charms , dealing with fortune tellers and even dancing . Hermits were forbidden from talking with townsfolk or presenting themselves in a particular manner . To make matters worse , no representatives were summoned from Rome so when Pope Sergius I was asked to approve of 102 cannons he not only refused but managed to use the militias of Rome and Ravenna against the Exarch Zacharias . The clemency of the pope allowed the Exarch of Ravenna to escape with his life . Upon hearing of this , Justinian is said to have gone into another one of his rages . He was already unpopular at the young age of 23 . His heavy handedness in extracting the tax money from the peasants and the rich made him deeply resented , especially with his use of torture , which included the use of fire and whips . It was therefore to no one ' s surprise ( though to many a Byzantine ' s delight ) that rebellion came from the ranks of the aristocracy . The revolt found a leader in a professional but disgraced soldier , Leontius . Non - dynastic : Leontius . Prisoner . Leontius was in prison when a monk once told him that he would one day wear the Imperial diadem . Such talk was not only dangerous for the monk ( who if discovered would have been blinded and exiled for treason ) but also dangerous for the man whose ears received — and preyed upon Leontius ' mind until in 695 ( after being released ) he immediately began a relatively unplanned coup . Fortunately for him many of his comrades had also been imprisoned ( suggesting that perhaps his entire unit may well have been disgraced ) so when he marched upon his former prison to release the inmates , many declared their support for him . Rise and Fall . Marching on to the Hagia Sophia , he was fortunate enough to find the support of the Patriarch Callinicus I — whose recent insults to the incumbent Emperor left him in fear of his life and with little choice . With the support of the fanatical Hippodrome Blue team , Leontius and his men overthrew Justinian II , cutting his nose off in the oriental process of " rhinokopia " and declaring himself as " Basileus " . Justinian ' s Father , though on more friendly terms with Leontius still lost his tongue and his nose as well . Leontius ' rule was both brief and a miserable failure . The armies of Islam were once more on the march and this time the Exarch of Carthage was in serious trouble . Earlier defeats had established Arab supremacy in the region . Leontius , despite his military background , had an unsuccessful expedition sent to Carthage . Rather than report their loss and face the inevitable wrath of the Emperor , the defeated troops decided to name one of their own as " Basileus " ( a German called Apsimar ) and with the support of the Hippodrome Green team ( a serious rival of the Blue team that promoted Leontius to the Imperial throne ) established Apsimar as " Basileus " Tiberius III . Non - dynastic : Tiberius III . Tiberius ' rule was equally short but slightly more impressive for his successful campaigning against the Saracens — indeed it seems that his Germanic heritage had given him the same appetite for war that had allowed many of his " barbarian " kind to conquer the Western Empire , with his troops reaching into Armenia and even Muslim - held Syria . But by that time in 705 , he was overthrown by military force . Justinian , who for ten years was in exile , returned . The Byzantine population could not have asked for a worse overthrow . Justinian II ( restored ) . Years in exile . After having been deposed by Leontius , Justinian escaped to the Khagan of the Khazars who welcomed him and even gave his sister as a wife to him . Renaming his wife Theodora he settled at Phanagoria at the entrance to the Sea of Azov where they could keep an eye on Imperial events . Justinian was forced to act when in 704 word reached that he was wanted dead or alive for a handsome reward . Such rumors were confirmed when a band of soldiers arrived at his location . Realizing that his life was in danger , he invited two of the officers ( whom he suspected as the assassins ) to his house and murdered them . Leaving his wife in the safety of her brother , he fled to Bulgaria , Byzantium ' s chief opponent in the West . There he secured a pact with the Bulgar King Tervel granting him the title of Caesar if he aided him in regaining the throne of Byzantium . Restoration & rule . In the spring of 705 , Constantinople found herself surrounded by yet another army of Slavs and Bulgars , led by Justinian . After three days of scouting his men found an abandoned conduit running across the walls and managed to slip inside . There he surprised the sleeping guards at the Palace of Blachernae . Within moments , the building was his and Tiberius fled to Bithynia whilst the citizens of the capital surrendered — the alternative would have been a savage sack that in the mind of the vengeful Justinian , was what it needed . The following day , Justinian was given the title of Caesar and a purple robe . With his coup successful , Justinian II set about bringing his wife back and settling the numerous scores he had with his disloyal subjects . Tiberius and his predecessor Leontius were both executed the previous day after a humiliating pelting at the Hippodrome . Next the Patriarch Callinicus , whose offence had led to his hasty support of Leontius and the crowning of both of Justinian ' s successors led to his blinding and exile to Rome . After that Justinian set about killing Tiberius ' brother , Heraclius who was perhaps the best general in the Empire . With him and his staff of officers dead , Byzantium ' s neighbours lost no time in exploiting the weakened army — suffering major defeats against the barbarian tribes near the mouth of the Danube and losing the vital stronghold of Tyana in Cappadocia . Expeditions of revenge . It can be said without hesitation that Justinian ' s return to power was nothing more than a sad epilogue to the Heraclian line , with revenge being the state ' s most highly prioritized policy . Ravenna . Bent upon making others suffer as he had , Justinian had an expedition sent against the Exarchate of Ravenna , for reasons which elude historians today — though sheer madness cannot be ruled out . Upon arriving there the expedition led by Theodore sacked the city whilst his men deceptively invited the officials to a banquet where they were seized and sent to Constantinople . Upon arrival they were met by Justinian , who had them all executed except the Archbishop , who nonetheless suffered a blinding and the usual exile — not being able to return until Justinian was in his grave . It was this execution that led to Ravenna being looted by Theodore and his men . In Rome however the mood was calmed by the Pope Constantine the Syrian . Relations between the Pope and the Emperor had greatly improved — with the Emperor kissing the Pope ' s feet and sending an impressive delegation before him to meet the Pope ( consisting of the Patriarch of Constantinople and Justinian ' s son and co - emperor ) . Arriving at Constantinople in 711 he came to an accord with Justinian finally approving half of the 102 canons still outstanding from the Quinisext Council ( dealing with the trivial matters he addressed before his exile ) and agreeing to drop the other , perhaps less important canons . Satisfied he allowed the Pope a safe journey to Rome . Cherson . Justinian then targeted his former place of exile in the Crimea . There his brother - in - law , the Khagan , had infringed on Imperial territory by establishing a Khazar governor of his own to run Cherson . Upon arriving there , the expedition set about doing its work — countless citizens were drowned ( apparently with weights attached ) and seven were roasted alive . The " Tudun " , the governor appointed by the Khagan was sent to Constantinople with 30 others . However , a storm destroyed his army and his fleet when he ordered it to return . Justinian is said to have greeted the news with great laughter . Another fleet was sent but the arrival of the Khagan ' s army made Justinian reconsider his move to a more diplomatic one . He decided to send the " Tudun " back to the Khagan with his apologies and had George of Syria to present the Imperial apology . The citizens of Cherson were naturally in no mood to hear any apology after what Justinian had done . When the Tudun died along the way , the Khazars took it upon themselves to send his 300 - strong escort to the afterlife with him . Overthrow . After the fiasco of the Cherson expedition , the citizens there proclaimed a new man , Bardanes ( an exiled General ) the " Basileus " of Byzantium . Justinian was enraged at these turn of events . Once more he began redirecting resources to another expedition under the Patriarch Maurus against Cherson , resources that could have been better spent against the Arabs or the Bulgars . The Khazars appeared at the scene preventing the expedition from destroying no more than two defense towers before being obliged to make terms . The Patriarch realized that returning to the capital in defeat would undoubtedly lead to a violent retirement at the hands of Justinian . Therefore in a similar case to Leontius and Tiberius ' usurpation , he defected and , with the army and navy under his command , declared his support for the renegade Bardanes , who changed his name to Philippicus . As Philippicus headed for the Capital Justinian was making his way to Armenia , a warzone between the Byzantines and Arabs . He reached as far as Nicomedia when attempting to turn back , he was caught at the twelfth mile stone of the Capital and executed on the spot . Philippicus had arrived before he could and was greeted with open arms at the capital . Theodora , the Khazar wife of Justinian II escaped to a nearby monastery with her son and former co - emperor Tiberius . The young boy was holding on to the True Cross when a soldier entered and forced his hand from it . It is said that the soldier then laid the Cross with great respect on the altar . Following this rather pious act , he then dragged the boy outside and beneath the porch of a nearby church , butchered the line of Heraclius into extinction forever .