Abbasid invasion of Asia Minor ( 782 ) The Abbasid invasion of Asia Minor in 782 was one of the largest operations launched by the Abbasid Caliphate against the Byzantine Empire . The invasion was launched as a display of Abbasid military might in the aftermath of a series of Byzantine successes . Commanded by the Abbasid heir - apparent , the future Harun al - Rashid , the Abbasid army reached as far as Chrysopolis , across the Bosporus from the Byzantine capital , Constantinople , while secondary forces raided western Asia Minor and defeated the Byzantine forces there . As Harun did not intend to assault Constantinople and lacked ships to do so , he turned back . The Byzantines , who in the meantime had neutralized the detachment left to secure the Abbasid army ' s rear in Phrygia , were able to trap Harun ' s army between their own converging forces . The defection of the Armenian general Tatzates , however , allowed Harun to regain the upper hand . The Abbasid prince sent for a truce and detained the high - ranking Byzantine envoys , who included Empress Irene ' s chief minister , Staurakios . This forced Irene to agree to a three - year truce and pay a heavy annual tribute . Irene then focused her attention to the Balkans , but warfare with the Arabs resumed in 786 , until mounting Arab pressure led to another truce in 798 , on terms similar to those of 782 . Background . Taking advantage of the internal difficulties of the Umayyad Caliphate that resulted from the civil wars of the 740s and the subsequent Abbasid Revolution , the Byzantines under Emperor Constantine V ( reign ed 741 – 775 ) were able to regain the initiative on their eastern borders from the Arabs , and pursued an aggressive strategy . With the gradual consolidation of the Abbasid regime in the 760s and 770s , the situation became more balanced : the Arabs resumed their large - scale raids deep into Asia Minor , although the Byzantines were still capable of major counterstrikes . Thus in 778 , the Byzantines , under Michael Lachanodrakon , seized the town of Germanikeia ( Ma ' rash ) , where they captured significant amounts of booty and took many Syrian Christians captive , and defeated an army sent against them by the Abbasid general Thumama ibn al - Walid . In the next year , the Byzantines took and razed the fortress city of Hadath , forcing Caliph al - Mahdi ( r . 775 – 785 ) to replace the rather passive Thumama with the veteran al - Hasan ibn Qahtaba . Hasan led over 30 , 000 troops in an invasion of Byzantine territory , but the Byzantines offered no opposition and withdrew to well - fortified towns and refuges , until a lack of supplies forced Hasan to return home without achieving much . In response to these Byzantine successes , Caliph al - Mahdi now resolved to take the field in person . On 12 March 780 , Mahdi departed Baghdad and via Aleppo marched to Hadath , which he refortified . He then advanced to Arabissus , where he left the army and returned to Baghdad . His son and heir Harun — better known by his " laqab " , or regnal name , al - Rashid — was left in charge of one half of the army , which raided the Armeniac Theme and took the small fort of Semaluos . Thumama , who had been entrusted with the other half , penetrated deeper into Asia Minor . He marched west as far as the Thracesian Theme , but was heavily defeated there by Lachanodrakon . In June 781 , as the Arab invasion force assembled at Hadath under Abd al - Kabir , a great - great - nephew of the Caliph Umar ( r . 634 – 644 ) again prepared to launch their annual raid , Empress Irene called up the thematic armies of Asia Minor and placed them under the eunuch " sakellarios " John . The Muslims crossed into Byzantine Cappadocia over the Pass of Hadath , and were met near Caesarea by the combined Byzantine forces under Lachanodrakon . The ensuing battle resulted in a costly Arab defeat , forcing Abd al - Kabir to abandon his campaign and retreat to Syria . This defeat infuriated the Caliph , who prepared a new expedition . Intended as a show of force and a clear display of the Caliphate ' s superiority , it was the largest army sent against Byzantium in the second half of the 8th century : it allegedly comprised 95 , 793 men , about twice the total Byzantine military establishment present in Asia Minor , and cost the Abbasid state some 1 . 6 million " nomismata " , almost as much as the Byzantine Empire ' s entire annual income . Harun was the nominal leader , but the Caliph took care to send experienced officers to accompany him . Campaign . On 9 February 782 , Harun departed Baghdad ; the Arabs crossed the Taurus Mountains by the Cilician Gates , and swiftly took the border fortress of Magida . They then advanced along the military roads across the plateau into Phrygia . There , Harun left his lieutenant , the " hadjib " al - Rabi ' ibn Yunus , to besiege Nakoleia and guard his rear , while another force , reportedly 30 , 000 men , under al - Barmaki ( an unspecified member of the powerful Barmakid family , probably Yahya ibn Khalid ) , was sent to raid the rich western coastlands of Asia Minor . Harun himself , with the main army , advanced to the Opsician Theme . The accounts of subsequent events in the primary sources ( Theophanes the Confessor , Michael the Syrian , and al - Tabari ) differ on the details , but the general course of the campaign can be reconstructed . According to Warren Treadgold , the Byzantine effort seems to have been led by Irene ' s chief minister , the eunuch Staurakios , whose strategy was to avoid an immediate confrontation with Harun ' s huge army , but wait until it had split up and advanced to meet its various detachments independently . The Thracesians under Lachanodrakon confronted al - Barmaki at a place called Darenos , but were defeated and suffered heavy losses ( 15 , 000 men according to Theophanes , 10 , 000 according to Michael the Syrian ) . The outcome of al - Rabi ' s siege of Nakoleia is unclear , but he was probably defeated ; Theophanes ' s phrasing may imply that the town was taken , but Michael the Syrian reports that the Arabs suffered great losses and failed to capture it , a version of events confirmed by hagiographic sources . Al - Tabari reports that part of the main army under Yazid ibn Mazyad al - Shaybani met a Byzantine force led by a certain Niketas who was " count of counts " ( perhaps the Count of the Opsician Theme ) , probably somewhere near Nicaea . In the ensuing battle , Niketas was wounded and unhorsed in single combat with the Arab general and forced to retire , probably to Nicomedia , where the imperial " tagmata " ( professional guard regiments ) under the Domestic of the Schools Anthony were assembled . Harun did not bother with them , and advanced to the town of Chrysopolis , across the Bosporus Strait from Constantinople itself . Lacking ships to cross the Bosporus , and with no intention of assaulting Constantinople in the first place , Harun probably intended this advance only as a show of force . Furthermore , despite his success so far , Harun ' s position was precarious , as the defeat of al - Rabi threatened his lines of communication with the Caliphate . Consequently , after plundering the Byzantine capital ' s Asian suburbs , Harun turned his army back , but during his march along the valley of the Sangarius River , east of Nicaea , he was surrounded by the forces of the " tagmata " under Anthony in his rear and of the Bucellarians under their general Tatzates to his front . Fortunately for him , at this point Tatzates , an Armenian prince who had defected from his Arab - ruled homeland to the Byzantines in 760 and was closely associated with the iconoclast regime of Constantine V , secretly made contact with him . Tatzates offered to aid Harun in exchange for a pardon and a safe return for himself and his family to his native Armenia . Theophanes explains Tatzates ' s actions with his hostility towards Irene ' s favourite , Staurakios , but this evidently masks a broader dissatisfaction with Irene ' s regime . As Ralph - Johannes Lilie writes , " Tatzates did not see any big opportunities for himself under the new regime and indeed used the good chance that the situation offered him . " Thus , when Harun asked for negotiations , Irene dispatched a delegation of three of her most senior officials : the Domestic Anthony , the " magistros " Peter , and Staurakios himself . Confident of their military position , they neglected to secure promises for their safety or hostages of their own , so that when they arrived in the Arab camp , they were made prisoners . Coupled with the treachery of Tatzates and the unreliability of the troops under his command , Irene was now forced to negotiate for their release , especially of her trusted aide Staurakios . The two states concluded a three - year truce in exchange for a heavy annual tribute — the Arab sources mention various amounts between 70 , 000 and 100 , 000 gold " nomismata " , while one also adds 10 , 000 pieces of silk . Tabari ' s account records that the tribute amounted to " ninety or seventy thousand " dinars " " , to be paid " at the beginning of April and in June every year " . In addition , the Byzantines were obliged to provide provisions and guides for Harun ' s army on its march home , and to hand over Tatzates ' s wife and property . Harun released all his captives ( 5 , 643 according to Tabari ) , but kept the rich plunder he had gathered , and returned to the Caliphate in September 782 . Tabari , in his account of the expedition , says that Harun ' s forces captured 194 , 450 " dinars " in gold and 21 , 414 , 800 " dirham s " in silver , killed 54 , 000 Byzantines in battle and 2 , 090 in captivity and took over 20 , 000 riding animals captive while slaughtering 100 , 000 cattle and sheep . Tabari also reports that the amount of plunder was such that " a work horse was sold for a " dirham " and a mule for less than ten " dirhams " , a coat of mail for less than a " dirham " , and twenty swords for a " dirham " " — at a time when one to two " dirhams " was the usual daily salary of a labourer or soldier . Aftermath . The successful Arab invasion had important repercussions in Byzantium . The outcome represented a major blow to Empress Irene ' s prestige , while Tatzates , a capable and veteran leader , was lost to the Empire and became the ruler of his native Armenia for the Abbasids . On the other hand , despite the humiliating peace treaty , Byzantium ' s losses were not excessive , especially considering the scale of the Arab attack , and Irene used the three years of the truce to strengthen her internal position : she seems to have dismissed most of the " old guard " of Constantine V ' s generals , with the long - serving and fanatically iconoclast Michael Lachanodrakon being the most prominent victim of this bloodless purge . In this way , Irene secured control over the military , and was able to refocus its efforts in expanding and consolidating Byzantine control over the Slavs of the Balkans . Despite the truce , the chronicler Ibn Wadih mentions Arab raids into Asia Minor for the years 783 , 784 and 785 . If true , then these would probably represent only minor affairs , as the main sources agree that the truce was mutually respected until spring 785 . In that year , as Irene had strengthened her hold over the army and was preparing to confront the iconoclasts on the domestic front , she decided to cease payment of the tribute , and hostilities recommenced . In early 786 , the Byzantines scored a major success , sacking and razing to the ground the fortress town of Hadath in Cilicia , which the Abbasids had spent the last five years turning into a major stronghold and military base for their cross - border expeditions . After the accession of Harun al - Rashid to the caliphal throne in the same year , however , the Abbasids regained the initiative . Arab pressure mounted , and in 798 Irene was forced to ask for a peace treaty that repeated the stipulations of the 782 truce .