 Marwan now launched a two @-@ pronged offensive against the Khazars : 30 @,@ 000 men under the governor of Derbent , Asid ibn Zafir al @-@ Sulami , advanced north along the coast of the Caspian Sea , while Marwan himself with the bulk of his forces crossed the Darial Pass . The two armies met at Samandar , and from there Marwan pushed on , reaching , according to some Arab sources , the Khazar capital of Atil ( al @-@ Bayda ' ) on the Volga . Most Arab sources contain few details on the campaign , but Ibn A 'tham reports that Marwan attacked the Slavs living in the region and took 40 @,@ 000 captives . As the Khazars avoided battle , he then sent a detachment of 40 @,@ 000 troops across the Volga under al @-@ Kawthar ibn al @-@ Aswad al- ' Anbari , which surprised the Khazars in a swamp . In the ensuing battle , the Arabs killed 10 @,@ 000 Khazars , including the tarkhan , and took 7 @,@ 000 captive . Thereupon the Khazar khagan himself is said to have requested peace and to have converted to Islam and recognized the Caliph 's authority . Marwan also took with him large numbers of Slav and Khazar captives , whom he resettled in the eastern Caucasus : some 20 @,@ 000 Slavs were settled at Kakheti , according to al @-@ Baladhuri , while the Khazars were resettled at al @-@ Lakz . The Slavs killed their Arab governor and fled north , but Marwan rode after them and killed them . 
