 In 730 , al @-@ Jarrah returned to the offensive through Tiflis and the Darial Pass . Arab sources report that he reached as far as the Khazar capital , al @-@ Bayda , on the Volga , but modern historians such as Blankinship consider this improbable . The Khazars launched a counterstroke under a certain <unk> , which forced al @-@ Jarrah to retreat south of the Caucasus once again to defend Albania . It is unclear whether the Khazars came through the Darial Pass or the Caspian Gates , but they managed to move around al @-@ Jarrah 's army at Bardha 'a and lay siege to Ardabil . The city was the capital of Adharbayjan , and the mass of the Muslim settlers and their families , some 30 @,@ 000 in total , lived within its walls . When al @-@ Jarrah learned of this , he led his army in a rapid march south and engaged the Khazars outside the city walls . There , after a three @-@ day battle on 7 – 9 December 730 , al @-@ Jarrah 's army of 25 @,@ 000 was all but annihilated by the Khazars under Barjik . Al @-@ Jarrah also fell and command passed to his brother al @-@ Hajjaj , who was unable to prevent the sacking of Ardabil . The 10th @-@ century historian Agapius of Hierapolis reports that the Khazars took as many as 40 @,@ 000 prisoners from the city , al @-@ Jarrah 's army , and the surrounding countryside . The Khazars raided the province at will , sacking <unk> and attacking other settlements , with some detachments reaching as far as Mosul in the northern Jazira , adjacent to the Umayyad metropolitan province of Syria . 
