 In the summer of 732 , Marwan led 40 @,@ 000 men north into Khazar lands . The accounts of this campaign are confused : Ibn A 'tham records that he reached Balanjar and returned to Derbent with much captured livestock , but the campaign is described in terms strongly reminiscent of Maslama 's expeditions in 728 and 731 , and its veracity is open to doubt . Ibn Khayyat on the other hand reports that Marwan led a far more limited campaign on the country immediately to the north of Derbent and then retired there to spend the winter . Marwan was more active in the south , where he raised Ashot III Bagratuni to the position of presiding prince of Armenia , effectively granting the country broad autonomy in exchange for the service of its soldiers alongside the Caliphate 's armies . This unique concession points , according to Blankinship , to the worsening manpower crisis faced by the Caliphate . At about the same time , the Khazars and Byzantines strengthened their ties and formalized their alliance against their common enemy with the marriage of Constantine V to the Khazar princess <unk> . 
