Abdallah ibn Ali Abdallah ibn Ali ibn Abdallah ibn al - Abbas ( ca . 712 – 764 CE ) was a member of the Abbasid dynasty , who played a leading role in its rise to power during the Abbasid Revolution . As governor of Syria , he consolidated Abbasid control over the province , eliminating the remnants of the Umayyad dynasty and suppressing pro - Umayyad uprisings . After the death of his nephew and first Abbasid Caliph , al - Saffah , in 754 , he launched a bid for the caliphal title against al - Saffah ' s brother , al - Mansur , but was defeated and imprisoned . He was killed in 764 . Role in the Abbasid Revolution . Abdallah was a member of the Abbasid family , and uncle to the first two Abbasid caliphs , al - Saffar ( reigned 749 – 754 ) and al - Mansur ( r . 754 – 775 ) . By early 749 , the anti - Umayyad uprising that had begun under Abu Muslim in Khurasan had prevailed in the eastern lands of the Caliphate , and the Khurasani armies swept west across Persia to the borders of Iraq . In October 749 , al - Saffah was proclaimed Caliph at Kufa , and quickly gained the acceptance of Abu Muslim and the Kufans , thereby forestalling an Alid bid for control of the Revolution . To cement Abbasid control , al - Saffah now appointed members of his own family to command the armies : his brother , the future al - Mansur , was sent to lead the Siege of Wasit , while Abdallah was sent to confront the Umayyad caliph Marwan II in the Jazira . Thus Abdallah held the supreme command in the decisive Battle of the Zab , where the Abbasid forces defeated the last Umayyad Caliph , Marwan II ( r . 744 – 750 ) , and led the pursuit of the latter , first to Syria , where he captured the Umayyad capital , Damascus , and then to Palestine , forcing Marwan to flee to Egypt . His brother Salih followed Marwan to Egypt , where the Umayyad ruler was captured and executed . Governorship of Syria and suppression of Umayyad risings . As the first Abbasid governor of Syria , Abdallah proved himself an implacable enemy of the Umayyads , vigorously persecuting the family ' s members . According to K . V . Zetterstéen , " he shrank from no method to exterminate them root and branch . During his stay in Palestine , he had about eighty of them murdered at one time . " So effective was this persecution , that only a single member of the dynasty , Marwan ' s grandson Abd al - Rahman ibn Mu ' awiya , managed to escape death and flee to al - Andalus , where he established a new Umayyad dynasty . This harsh suppression , and the depredations of the victorious Khurasani soldiers , soon provoked an uprising of the Syrian tribes , led by the governor of " Jund Qinnasrin " , Abu ' l - Ward ibn al - Kawthar . To them soon came Abu Muhammad , a descendant of Caliph Mu ' awiya I , who put himself forward as a candidate for reviving the Umayyad Caliphate . The rebels were at first successful , routing an Abbasid amry under Abdallah ' s brother Abd al - Samad near Qinnasrin , but Abdallah finally dealt a heavy defeat on them at Marj al - Akhram in late 750 . Abu ' l - Ward himself fell , while Abu Muhammad fled tot he desert . A nephew of Abu Muhammad , al - Abbas ibn Muhammad , rose up in Aleppo shortly after , but al - Mansur , who governed the Jazira , sent troops that had quelled the uprising before Abdallah could arrive . Abdallah then marched on to the frontier fortress of Sumaysat , where disparate Umayyad loyalists had gathered under Ishaq ibn Muslim al - Uqayli . In the event , a negotiated settlement was reached between Ishaq and al - Mansur , and many of the pro - Umayyad leaders became accepted in the ranks of the Abbasids . Another uprising , headed by Aban ibn Mu ' awiya , a grandson of Hisham ibn Abd al - Malik , erupted in summer 751 near Sumaysat , forcing Abdallah to interrupt a raid into Byzantine territories to suppress it . Another Umayyad loyalist , Abd al - Samad ibn Muhammad ibn al - Hajjaj ibn Yusuf , managed to escape defeat and capture until 755 . Bid for the Caliphate . Despite the recurrence of pro - Umayyad revolts in the Jazira , over the next few years Abdallah was apparently able to secure the loyalty of the Syrian tribal nobility , and the province remained mostly calm . By the time of al - Saffah ' s death in June 754 , he ranked , along with al - Mansur and the viceroy of the east , Abu Muslim , as one of the three most powerful men in the Caliphate . Al - Saffah died on his way to Mecca , and in his deathbed he nominated al - Mansur as his heir . At the time , Abdallah was preparing a major campaign against the Byzantine Empire , and had assembled a large army to this purpose . Upon receiving news of the al - Saffah ' s death , he proclaimed himself as Caliph , claiming that al - Saffah had promised him the succession as a reward for his role in the overthrow of Marwan II . The veracity of Abdallah ' s claim and the level of legitimacy he enjoyed vis - à - vis al - Mansur is difficult to assess following the prevalence of hostile traditions after his defeat , but , as P . Cobb comments , " what all accounts agree on is that the succession to al - Saffah was not solidly secured before his death " , and there are indications that Abdallah " had portrayed himself as an obvious successor [ . . . ] in the few years prior to al - Saffah ' s death . " Nevertheless , he enjoyed broad support in Syria , both by the native Syro - Jaziran troops and the Syrian elites who sought to regain the privileged position they had held under the Umayyads , as well as the Khurasani soldiers he had commanded during the Revolution . As Abdallah ' s army began its march on Iraq , al - Mansur turned to Abu Muslim for support . Although the Caliph distrusted Abu Muslim ' s power , the fact that he was universally popular with the Khurasani soldiers of the Revolution made him an ideal candidate to confront Abdallah and rally most of the Khurasani soldiery , which formed the regime ' s main pillar , to the Caliph ' s side . The two armies met at Nisibis in November 754 . Abdallah ' s army was riven with doubt , as the Khurasanis were loath to fight Abu Muslim — indeed , according to K . V . Zetterstéen , Abdallah " is said to have killed 17 , 000 Khurasanis in his army , because he feared they would never fight against Abu Muslim " — and the Syrians still resented their defeat at Abdallah ' s hands at the Zab . In the words of Hugh N . Kennedy , Abdallah " suspected treachery all round and fled before the battle really developed " , seeking refuge in Basra , where another brother of his , Sulayman , was governor . Despite the victory just gained in his name , the wily al - Mansur moved quickly to eliminate Abu Muslim , his chief remaining rival . A few months later , Abu Muslim was persuaded to come to the caliphal court , where he was murdered . Abdallah remained in Basra under his brother ' s protection until the latter was dismissed , two years later . Abdallah was now imprisoned on al - Mansur ' s orders , until , in 764 , he was " taken into a house that had been purposely undermined ; it fell down on him and buried him under the ruins " ( K . V . Zetterstéen ) . At the time of his death , he was said to be 52 years old . Despite Abdallah ' s rebellion , he was succeeded in Syria by his brother Salih and his family , who remained as the paramount Abbasid potentates in the province for the next half - century .