Thomas the Slav Thomas the Slav ( 760 – October 823 AD ) was a 9th - century Byzantine military commander , most notable for leading a wide - scale revolt in 821 – 23 against Emperor Michael II the Amorian ( ruled 820 – 29 ) . An army officer of Slavic origin from the Pontus region ( now north - eastern Turkey ) , Thomas rose to prominence , along with the future emperors Michael II and Leo V the Armenian ( r . 813 – 820 ) , under the protection of general Bardanes Tourkos . After Bardanes ' s failed rebellion in 803 , Thomas fell into obscurity until Leo V ' s rise to the throne , when Thomas was raised to a senior military command in central Asia Minor . After the murder of Leo and usurpation of the throne by Michael the Amorian , Thomas revolted , claiming the throne for himself . Thomas quickly secured support from most of the themes ( provinces ) and troops in Asia Minor , defeated Michael ' s initial counter - attack and concluded an alliance with the Abbasid Caliphate . After winning over the maritime themes and their ships as well , he crossed with his army to Europe and laid siege to Constantinople . The imperial capital withstood Thomas ' s attacks by land and sea , while Michael II called for help from the Bulgarian ruler Omurtag . Omurtag attacked Thomas ' s army , but although repelled , the Bulgarians inflicted heavy casualties on Thomas ' s men , who broke and fled when Michael took to the field a few months later . Thomas and his supporters sought refuge in Arcadiopolis , where he was soon blockaded by Michael ' s troops . In the end , Thomas ' s supporters surrendered him in exchange for a pardon , and he was executed Thomas ' s rebellion was one of the largest in the Byzantine Empire ' s history , but its precise circumstances are unclear due to competing historical narratives , which have come to include claims fabricated by Michael to blacken his opponent ' s name . Consequently , various motives and driving forces have been attributed to Thomas and his followers . As summarized by the " Oxford Dictionary of Byzantium " , " Thomas ' s revolt has been variously attributed to a reaction against Iconoclasm , a social revolution and popular uprising , a revolt by the Empire ' s non - Greek ethnic groups , Thomas ' s personal ambitions , and his desire to avenge Leo V . " Its effects on the military position of the Empire , particularly vis - à - vis the Arabs , are also disputed . Early life and career . The 11th century " Theophanes Continuatus " states that Thomas was descended from South Slavs resettled in Asia Minor by successive Byzantine emperors , while the 10th century chronicler Genesios calls him " Thomas from Lake Gouzourou , of Armenian race " . Most modern scholars support his Slavic descent and believe his birthplace to have been near Gaziura in the Pontus . Hence his epithet of " the Slav " , which has been applied to him only in modern times . Nothing is known about his family and early life , except that his parents were poor and that Thomas himself had received no education . Given that he was between 50 and 60 years old at the time of the rebellion , he was probably born around 760 . Two different accounts of Thomas ' s life are recounted in both Genesios and " Theophanes Continuatus " . According to the first account , Thomas first appeared in 803 accompanying general Bardanes Tourkos , and pursued a military career until launching his revolt in late 820 . In the second version , he came to Constantinople as a poor youth and entered the service of a man with the high court rank of " patrikios " . Then , discovered trying to commit adultery with his master ' s wife , Thomas fled to the Arabs in Syria , where he remained for 25 years . Pretending to be the murdered emperor Constantine VI ( r . 780 – 797 ) , he then led an Arab - sponsored invasion of Asia Minor , but was defeated and punished . Classical and Byzantine scholar J . B . Bury tried to reconcile the two narratives , placing Thomas ' s flight to the Abbasid Caliphate at around 788 and then having him return to Byzantine service before 803 , while the Russian scholar Alexander Vasiliev interpreted the sources as implying that Thomas fled to the Caliphate at Constantine VI ' s deposition in 797 , and that his participation in Bardanes ' s revolt must be discounted entirely . The second version of Thomas ' s story is explicitly preferred by Genesios and " Theophanes Continuatus " , and is the only one recorded in 9th century sources , namely the chronicle of George the Monk and the " Life of Saints David , Symeon , and George of Lesbos " . Nevertheless , the French Byzantinist Paul Lemerle came to consider it an unreliable later tradition created by Michael II to discredit Thomas , and rejected it altogether , preferring to rely on the first account alone . Most modern scholars follow him in this interpretation . The first tradition relates that Thomas served as a " spatharios " ( staff officer ) to Bardanes Tourkos , the " monostrategos " ( " single - general " , i . e . commander - in - chief ) of the eastern themes , who in 803 rose in rebellion against Emperor Nikephoros I ( r . 802 – 811 ) . Alongside Thomas were two other young " spatharioi " in Bardanes ' s retinue , who formed a fraternal association : Leo the Armenian , the future Leo V , and Michael the Amorian , the future Michael II . According to a later hagiographic tradition , before launching his revolt , Bardanes , in the company of his three young protégés , is said to have visited a monk near Philomelion who was reputed to foresee the future . The monk predicted what would indeed happen : that Bardanes ' s revolt would fail , that Leo and Michael would both become emperors , and that Thomas would be acclaimed emperor and killed . When Bardanes did in fact rise up , he failed to win any widespread support . Leo and Michael soon abandoned him and defected to the imperial camp and were rewarded with senior military posts . Thomas alone remained loyal to Bardanes until his surrender . In the aftermath of Bardanes ' s failure , Thomas disappears from the sources for ten years . Bury suggests that he fled ( for a second time according to his interpretation ) to the Arabs , a view accepted by a number of other scholars , such Romilly James Heald Jenkins . The historian Warren Treadgold , however , argues that Thomas stayed in the empire and may have even remained in active military service , and explains his obscurity by Thomas ' s association with Bardanes , which hampered his career . In July 813 , Leo the Armenian became emperor and quickly rewarded his old companions , giving them command over elite military forces . Michael received the " tagma " of the Excubitors ( one of the professional guard cavalry regiments stationed around Constantinople ) , and Thomas the " tourma " ( division ) of the " Foederati " , stationed in the Anatolic Theme . Rebellion . Background and motives . On Christmas Day 820 , Leo was murdered in the palace chapel by officials under the direction of Michael the Amorian , who became emperor . At about the same time , Thomas launched a rebellion in the Anatolic Theme . Sources are divided on the exact chronology and motives of the revolt . George the Monk , the hagiographic sources , and a letter from Michael II to the western emperor Louis the Pious claim that Thomas had risen up against Leo before Michael ' s usurpation . This chronology is followed by later chroniclers like Genesios , " Theophanes Continuatus " , and Skylitzes , as well as a number of modern scholars like John B . Bury and Alexander Kazhdan . In his study of Thomas and the revolt , Paul Lemerle dismisses this timeline as a later attempt by Michael to justify his revolt as a response to Leo ' s failure to suppress the rebellion , and to exculpate himself of the early defeats suffered by the imperial forces . Some recent studies follow Lemerle and prefer the account of Symeon Logothetes — generally considered the most accurate of the 10th century sources — according to which Thomas rebelled a few days after the murder of Leo and in reaction to it . The empire became divided in a struggle that was less a rebellion against the established government and more a contest for the throne between equal contenders . Michael held Constantinople and the European provinces , controlled the imperial bureaucracy , and had been properly crowned by the Patriarch , but he had come to the throne through murder , while Thomas gained support and legitimacy through his claim to avenge the fallen Leo , and he won the backing of themes both in Asia and later in Europe . Thomas was a well - known , popular , and respected figure in Asia Minor , where Leo V had enjoyed considerable support . Michael , on the other hand , was virtually unknown outside the capital ; his military record was unremarkable , he was uneducated and coarse of manner , his stutter earned him ridicule , and he was reputed to sympathize with the heretical religious sect of the Athinganoi , to which his family had belonged . Byzantine accounts of Thomas ' s rebellion state that he did not in fact claim the throne under his own name but assumed the identity of Emperor Constantine VI , who had been deposed and murdered by his mother , Irene of Athens , in 797 . Most modern scholars follow Lemerle , who dismisses this as yet another later fabrication . It is possible that this story may originate from Thomas choosing to be crowned under the regnal name of " Constantine " , but there is no evidence for such an act . The possible appropriation of Constantine VI ' s identity is linked in some sources with the statement that Thomas was a rumoured supporter of iconolatry , as opposed to Michael ' s support for iconoclasm : it was under Constantine VI that veneration of the icons was restored . Nevertheless , the ambiguous phrasing of the sources , the iconoclast leanings of many themes in Asia Minor , and Thomas ' s alliance with the Arabs seem to speak against any open commitment to icon worship on his part . Given Michael II ' s conciliatory approach during his early reign , the icon worship controversy does not seem to have been a major issue at the time , and in the view of modern scholars most probably did not play a major role in Thomas ' s revolt . The image of Thomas as an iconophile champion opposed to the iconoclast Michael II in later , Macedonian - era sources was probably the result of their own anti - iconoclast bias . Warren Treadgold holds that Thomas ' s claim to be Constantine VI , if true , may have been little more than a tale circulated to win support , and that Thomas pursued a " studied ambiguity " towards icons , designed to attract support from iconophiles . In Treadgold ' s words , " Thomas could be all things to all men until he had conquered the whole empire , and then he would have time enough to disappoint some of his followers " . " Theophanes Continuatus " also reports that under Thomas , " the servant raised his hand against his master , the soldier against his officer , the captain against his general " . This has led some scholars , chiefly Alexander Vasiliev and George Ostrogorsky , to regard Thomas ' s revolt as an expression of widespread discontent among the rural population , which suffered under heavy taxation . Others , notably Lemerle , dismiss rural discontent as a primary factor during the revolt . Genesios and other chroniclers further state that Thomas won the support of " Hagarenes , Indians , Egyptians , Assyrians , Medians , Abasgia ns , Zichs , Iberians , Kabirs , Slavs , Huns , Vandals , Getae , the sectarians of Manes , Laz , Alania ns , Chaldia ns , Armenians and every kind of other peoples " . This has led to modern claims that Thomas ' s rebellion represented an uprising of the empire ' s non - Greek ethnic groups , but according to Lemerle , this exaggerated account is yet another piece of hostile disinformation . It is almost certain , however , that Thomas could count on support among the empire ' s Caucasian neighbours , for the presence of Abasgians , Armenians , and Iberians in his army is mentioned in the near - contemporary letter of Michael II to Louis the Pious . The reasons for this support are unclear ; Thomas may have made unspecified promises , but Lemerle suggests that the Armenians might have in part been motivated by revenge for Leo , their murdered kinsman . Outbreak and spread of the revolt in Asia Minor . As commander of the " Foederati " , Thomas was based at Amorion , the capital of the Anatolic Theme . Although junior to the theme ' s " strategos " ( military governor ) , his proclamation received widespread support throughout Asia Minor . Within a short time , all the Asian themes supported Thomas , except for the Opsician Theme under the patrician Katakylas , a nephew of Michael II , and the Armeniac Theme , under its " strategos " , Olbianos . The Thracesian Theme wavered between the two rivals , but finally threw its support behind Thomas . More than two - thirds of the empire ' s Asian army eventually aligned with Thomas , while the defection of the provincial tax officials provided him with much - needed revenue . Michael ' s first response was to order the Armeniac army to attack Thomas . The Armeniacs were easily defeated in battle and Thomas proceeded through the eastern parts of the Armeniac Theme to occupy the frontier region of Chaldia . Thomas ’ s conquest of the Armeniac province was left incomplete because the Abbasids , taking advantage of the Byzantine civil war , launched raids by land and sea against southern Asia Minor , where Thomas had left few troops behind . Instead of returning to face these raids , Thomas launched a large - scale invasion of his own against Abbasid territory in spring 821 , either in Syria ( according to Bury and others ) or in Arab - held Armenia ( according to Treadgold ) . Thomas then sent an emissary to the Caliph al - Ma ' mun , who was sufficiently impressed by Thomas ' s show of force to receive his proposals , especially in view of the Caliphate ' s own problems with the rebellion of the Khurramites under Babak Khorramdin . Thomas and Ma ' mun concluded a treaty of peace and mutual alliance . The Caliph allowed Thomas to recruit men from Arab - held territories , and gave leave for him to cross the border and travel to Arab - held Antioch , where he was crowned emperor by the iconophile Patriarch of Antioch , Job . In exchange , Thomas is said to have promised to cede unspecified territories and become a tributary vassal of the Caliph , though the agreement ' s exact terms are unclear . At about the same time , Thomas adopted an young man of obscure origin , whom he named Constantius and made his co - emperor . Meanwhile , Michael II tried to win support among the iconophiles by appointing a relative of his as Archbishop of Ephesus , but his plan failed when the latter refused to be consecrated by the avowedly iconoclast Patriarch Antony I Kassimates . In an effort to consolidate his hold on the two Asian themes still loyal to him , Michael proclaimed a 25 percent reduction in taxes for 821 – 822 . By summer 821 , Thomas had consolidated his position in the East , though the Opsician and Armeniac themes still eluded him . He set his sights on the ultimate prize , Constantinople , the possession of which alone conferred full legitimacy to an emperor . Thomas assembled troops , gathered supplies , and built siege machines . To counter the powerful Imperial Fleet stationed in the capital , he built new ships to augment his existing fleet , which came from the Cibyrrhaeot and Aegean Sea naval themes , and possibly included task forces from the theme of Hellas . Thomas recalled Gregory Pterotos , a general and nephew of Leo V who had been exiled on the island of Skyros by Michael , and gave him command of the fleet . By October , the thematic fleets loyal to Thomas had finished assembling at Lesbos , and Thomas ' s army began marching from the Thracesian Theme towards Abydos , where he intended to cross over into Europe . At this point , Thomas suffered his first reversal of fortune : before his departure for Abydos , he had sent an army under his adoptive son Constantius against the Armeniacs . Constantius was ambushed by " strategos " Olbianos and killed , although the army was able to withdraw with relatively few casualties . Constantius ' s severed head was sent to Michael , who dispatched it to Thomas at Abydos . Thomas was undaunted by this relatively minor setback , and crossed over into Europe some time in late October or early November . There , Constantius was soon replaced as co - emperor by another obscure individual , a former monk whom Thomas also adopted and named Anastasius . Siege of Constantinople . Anticipating Thomas ' s move , Michael had gone out at the head of an army to the themes of Thrace and Macedonia in Constantinople ' s European hinterland and strengthened the garrisons of several fortresses there to secure the loyalty of their populace . When Thomas landed , the people of the European themes welcomed him with enthusiasm , and Michael was forced to withdraw to Constantinople . Volunteers , including many Slavs , flocked to Thomas ' s banner . As he set out towards Constantinople , chroniclers recount that his army swelled to some 80 , 000 men . The capital was defended by the imperial " tagma ta " , augmented by reinforcements from the Opsician and Armeniac themes . Michael had ordered the city walls to be repaired , and chained off the entrance to the Golden Horn , while the Imperial Fleet further guarded the capital from the sea . Nevertheless , judging from Michael ' s passive stance , his forces were inferior to Thomas ' s ; Warren Treadgold estimates Michael ' s army to have numbered approximately 35 , 000 men . Thomas ' s fleet arrived at the capital first . Facing no opposition from the Imperial Fleet , the rebels broke or unfastened the chain and entered the Golden Horn , taking station near the mouths of the Barbysos river , where they awaited the arrival of Thomas and his army . Thomas arrived in early December . The sight of his huge force did not cow the capital ' s inhabitants : unlike the provinces , the capital ' s citizens and garrison stood firmly behind Michael . To further encourage his troops , Michael had his young son Theophilos lead a procession along the walls , carrying a piece of the True Cross and the mantle of the Virgin Mary , while a large standard was hoisted on top of the Church of St . Mary at Blachernae , in full view of both armies . After subduing the cities around the capital , Thomas resolved to attack Constantinople from three sides , perhaps hoping his assault would impress its inhabitants or lead to defections . His deputies Anastasius and Gregory Pterotos would attack the Theodosian land and sea walls , respectively , while he would lead the main attack against the less formidable defenses protecting Blachernae . All of Thomas ' s forces were amply supplied with siege engines and catapults , and his fleet fielded quantities of Greek fire in addition to large shipborne catapults . Each of Thomas ' s attacks failed : the defenders ' artillery proved superior and kept Thomas ' s engines away from the land walls , while adverse winds hindered the fleet from taking any meaningful action . Deciding that operations in the midst of winter were hazardous and unlikely to succeed , Thomas suspended all further attacks until spring and withdrew his army to winter quarters . Michael used the respite to ferry in additional reinforcements from Asia Minor and repair the walls of Blachernae . When Thomas returned in spring , he decided to focus his attack on the Blachernae sector . Before the offensive , Michael himself ascended the walls and addressed Thomas ' s troops , exhorting them to abandon their commander and promising amnesty if they would defect . Thomas ' s army viewed the plea as a sign of weakness , and advanced confidently to begin the assault , but as they neared the wall , the defenders opened the gates and attacked . The sudden onslaught drove back Thomas ' s army ; at the same time , the Imperial Fleet defeated Thomas ' s ships , whose crews broke and fled to the shore in panic . This defeat diminished Thomas ' s naval strength , and although he continued blockading the capital by land , the loss demoralized his supporters , who began defecting . Gregory Pterotos , whose family was in Michael ' s hands , resolved to desert Thomas , followed by a small band of men loyal to him . He departed the rebel camp , headed west , and sent a monk to inform Michael of his defection , but the monk failed to circumvent the blockade and reach the capital . Upon learning of this defection , Thomas reacted quickly : with a select detachment , he followed Gregory , defeated his troops and killed the deserter . Thomas exploited this small victory for all it was worth , widely proclaiming that he had defeated Michael ' s troops " by land and sea " . He sent messages to the themes of Greece , whose support had been lukewarm until that point , demanding additional ships . The themes responded forcefully , sending their squadrons , allegedly numbering 350 vessels , to join him . Thus reinforced , Thomas decided to launch a two - pronged assault against Constantinople ' s sea walls , with his original fleet attacking the wall of the Golden Horn , and the new fleet attacking the south coast , looking towards the Sea of Marmara . Michael , however , did not remain idle : his own fleet attacked the thematic force soon after it arrived at its anchorage in Byrida . Using Greek fire , the Imperial Fleet destroyed many of the rebel vessels and captured most of the remaining ships . Only a few managed to escape and rejoin Thomas ' s forces . Through this victory , Michael secured control of the sea , but Thomas ' s army remained superior on land and continued its blockade of Constantinople . Minor skirmishes ensued for the remainder of the year , with Michael ' s forces sallying forth from the city to attack Thomas ' s forces . Although both sides claimed minor successes in these clashes , neither was able to gain a decisive advantage . Michael turned to the empire ' s northern neighbour , Bulgaria , for help . The two states were bound by a 30 - year treaty signed under Leo V , and the Bulgarian ruler , khan Omurtag ( r . 814 – 831 ) , was happy to respond to Michael ' s request for assistance . A later tradition , reported by Genesios and Theophanes Continuatus , holds that Omurtag acted of his own accord and against Michael ' s will , but this is almost universally rejected as a version started or at least encouraged by Michael , who did not wish to be seen encouraging " barbarians " to invade the empire . The Bulgarian army invaded Thrace , probably in November 822 ( Bury believes that the Bulgarian attack occurred in spring 823 ) , and advanced towards Constantinople . Thomas raised the siege , and marched to meet them with his army . The two armies met at a plain with an aqueduct near Heraclea ( hence known as the Battle of Kedouktos in the Byzantine sources ) . The accounts of the subsequent battle differ : the later sources state that Thomas lost the battle , but the near - contemporary George the Monk states that Thomas " killed many Bulgarians " . Given the lack of Bulgarian activity after the battle , most modern scholars ( with the notable exception of Bury ) believe that Thomas won the battle . Defeat and death of Thomas , end of the revolt . Thomas was unable to resume the siege : aside from the heavy casualties his army likely suffered , his fleet , which he had left behind in the Golden Horn , surrendered to Michael during his absence . Thomas set up camp at the plain of Diabasis , spending winter and early spring some west of Constantinople . While a few of his men deserted , the bulk remained loyal . Finally , in late April or early May 823 , Michael marched with his troops against Thomas , accompanied by the generals Olbianos and Katakylas with new troops from Asia Minor . Thomas marched to meet them and planned to use a stratagem to outwit his opponents : his men , ostensibly demoralized , would pretend to flee , and when the imperial army broke ranks to pursue them , they would turn back and attack . However , Thomas ' s troops were by now weary of the prolonged conflict , and their submission was unfeigned . Many surrendered to Michael , while others fled to nearby fortified cities . Thomas sought refuge in Arcadiopolis with a large group ; his adopted son Anastasius went with some of Thomas ' s men to Bizye , and others fled to Panium and Heraclea . Michael blockaded Thomas ' s cities of refuge but organized no assaults , instead aiming to capture them peacefully by wearing out their defenders . His strategy was motivated by the political and propaganda expedient of appearing merciful — " in order to spare Christian blood " , as Michael himself put it in his letter to Louis the Pious — but also , according to the chroniclers , by fear of demonstrating to the Bulgarians that the Byzantine cities ' fortifications could fall to attack . In Asia Minor , Thomas ' s partisans hoped to lure Michael away by allowing the Arabs free passage to raid the provinces of Opsikion and Optimaton , which were loyal to the emperor . Michael was unmoved and continued the blockade . His troops barred access to Arcadiopolis with a ditch . To conserve supplies , the blockaded troops sent away women and children , followed by those too old , wounded , or otherwise incapable of bearing arms . After five months of blockade , Thomas ' s loyalists were eventually forced to eat starved horses and their hides . Some began deserting by lowering themselves with ropes over the city walls or jumping from them . Thomas sent messengers to Bizye , where the blockade was less close , to arrange a relief attempt by Anastasius . Before anything could be done , however , the exhausted troops at Arcadiopolis surrendered their leader in exchange for an imperial pardon . Thomas was delivered to Michael seated on a donkey and bound in chains . He was prostrated before the emperor , who placed his foot on his defeated rival ' s neck and ordered his hands and feet cut off and his corpse impaled . Thomas pleaded for clemency with the words " Have mercy on me , oh True Emperor ! " Michael only asked his captive to reveal whether any of his own senior officials had had dealings with Thomas . Before Thomas could respond , the Logothete of the Course , John Hexaboulios , advised against hearing whatever claims a defeated rebel might make . Michael agreed , and Thomas ' s sentence was carried out immediately . When the inhabitants of Bizye heard of Thomas ' s fate , they surrendered Anastasius , who suffered the same fate as Thomas . In Panium and Heraclea , Thomas ' s men held out until an earthquake struck in February 824 . The tremor severely damaged the wall of Panium , and the city surrendered . The damage at Heraclea was less severe , but after Michael landed troops at its seaward side , it too was forced to surrender . In Asia Minor , Thomas ' s loyalists mostly submitted peacefully , but in the Cibyrrhaeot Theme , resistance lingered until suppressed by " strategos " John Echimos . In the Thracesian theme , Thomas ' s soldiers turned to brigandage . The most serious opposition was offered in central Asia Minor by two officers , who had possibly served Thomas as " strategoi " : Choireus , with his base at Kaballa northwest of Iconium , and Gazarenos Koloneiates , based at Saniana , southeast of Ancyra . From their strongholds , they spurned Michael ' s offer of a pardon and the high title of " magistros " and raided the provinces that had gone over to him . Soon , however , Michael ' s agents persuaded the inhabitants of the two forts to shut their gates against the officers . Choireus and Koloneiates then tried to seek refuge in Arab territory but were attacked en route by loyalist troops , captured , and crucified . Aftermath and effects . The end of Thomas the Slav ' s great rebellion was marked by Michael II ' s triumph , held in May 824 in Constantinople . While he executed Thomas ' s volunteers from the Caliphate and perhaps also the Slavs , the sheer number of individuals involved , the necessity of appearing clement and sparing with Christian lives , and the need to restore internal tranquillity to his realm compelled Michael to treat Thomas ' s defeated partisans with leniency : most were released after being paraded in the Hippodrome during his celebration , and only the most dangerous were exiled to remote corners of the empire . In an effort to discredit his opponent , Michael authorized an " official " and heavily - distorted version of Thomas ' s life and revolt . The document was written by the deacon Ignatios and published in 824 as " Against Thomas " . This report quickly became the commonly - accepted version of events . Thomas failed in spite of his qualities and the widespread support he had gained , which brought him control of most of the empire . Lemerle holds that several factors played a role in his defeat : the Asian themes he did not subdue supplied reinforcements to Michael ; Thomas ' s fleet performed badly ; and the Bulgarian offensive diverted him away from the capital and weakened his army . But the most decisive obstacles were the impregnable walls of Constantinople , which ensured that an emperor who controlled Constantinople could only be overthrown from within the city . Thomas ' s rebellion was the " central domestic event " of Michael II ' s reign , but it was not very destructive in material terms : except for Thrace , which had suffered from the prolonged presence of the rival armies and the battles fought there , the larger part of the empire was spared the ravages of war . The Byzantine navy suffered great losses , with the thematic fleets in particular being devastated , while the land forces suffered comparatively few casualties . This is traditionally held to have resulted in a military weakness and internal disorder which was swiftly exploited by the Muslims : in the years after Thomas ' s rebellion , Andalusian exiles captured Crete and the Tunisian Aghlabids began their conquest of Sicily , while in the East , the Byzantines were forced to maintain a generally defensive stance towards the Caliphate . More recent scholarship has disputed the degree to which the civil war was responsible for Byzantine military failures during these years , citing other reasons to explain them : Warren Treadgold opines that the empire ' s military forces recovered fairly quickly , and that incompetent military leadership coupled with " the remoteness of Sicily , the absence of regular troops on Crete , the simultaneity of the attacks on both islands , and the government ' s long - standing lack of interest in sea - power " were far more responsible for the loss of the islands .