 Since the nascent Caliphate regarded itself as the heir of the Sassanid ( and to a lesser extent , Byzantine ) tradition and " civilizational consciousness " , the Arab caliphs also adopted the notion that , in the words of the historian Gerald Mako , it was their duty " to protect the settled , i.e. the civilized world from the northern barbarian " . To this imperative was added the Muslim concept of division of the world into the " House of Islam " ( Dar al @-@ Islam ) and the " House of War " ( Dar al @-@ Harb ) , to which the pagan Turkic nomads were consigned . The two armies consequently represented two different military philosophies . While the Umayyad armies disposed of a sizeable cavalry contingent , both light and heavy , their mainstay was the infantry , to the extent that in battle the Arab cavalry was often limited to skirmishing during the initial phases , before dismounting and fighting on foot . The Khazars on the other hand , although they had adopted elements of the civilizations of the south and possessed towns , remained a largely tribal and semi @-@ nomadic power . Like their Central Asian counterparts , they practiced a highly mobile form of warfare , relying on their highly skilled and hardy cavalry . As the historian Khalid Yahya Blankinship writes , " the Khazars were to prove difficult opponents for the Muslims , perhaps partly because their state was not highly organized and thus did not have a center whose fall would bring about a sudden collapse and rapid surrender " . The eastern Caucasus range became the main theatre of the Arab – Khazar conflict , with the Arab armies aiming to gain control of Derbent ( known in Arabic as Bab al @-@ Abwab , " Gate of Gates " ) and the Khazar cities of Balanjar and Samandar , whose location has yet to be established with certainty by modern researchers . Both of the latter are referred to as Khazar capitals by different Arab writers , and may have functioned as winter and summer capitals respectively . It was only later , under the impact of the Arab attacks , that the Khazars moved their capital further north , to Atil on the mouths of the Volga . 
