▁and ▁their ▁Kh azar ▁al lies ▁approached ▁the ▁C asp ian ▁G ates ▁at ▁Der b ent . ▁This ▁newly ▁built ▁strong hold ▁was ▁the ▁only ▁gate ▁to ▁the ▁fert ile ▁land ▁of ▁Ag h van ia ▁( mod ern - day ▁A zer ba ij an ). ▁Lev ▁G um ile v ▁obser ves ▁that ▁the ▁light ly ▁armed ▁milit ia ▁of ▁Ag h van ia ▁was ▁no ▁match ▁against ▁the ▁h ord es ▁of ▁heavy ▁caval ry ▁led ▁by ▁T ong ▁Y ab g hu . ▁His ▁troops ▁storm ed ▁Der b ent ▁and ▁sw ar med ▁over ▁Ag h van ia , ▁pl und ering ▁it ▁thoroughly . ▁The ▁fall ▁and ▁s ack ▁of ▁Der b ent ▁was ▁described ▁in ▁detail ▁by ▁the ▁Armen ian ▁historian ▁Mov s es ▁K ag ank at vat si , ▁thought ▁to ▁have ▁been ▁an ▁e y ew it ness ▁to ▁the ▁event : ▁ ▁The ▁fall ▁of ▁the ▁for tr ess ▁that ▁had ▁been ▁considered ▁im pre gn able ▁spark ed ▁pan ic ▁all ▁over ▁the ▁country . ▁Ag h van ian ▁forces ▁with d rew ▁to ▁their ▁capital , ▁Part av , ▁from ▁wh ence ▁they ▁made ▁for ▁the ▁C au cas us ▁Mountains . ▁The ▁Gö kt ür ks ▁and ▁Kh az ars ▁over to ok ▁them ▁near ▁the ▁village ▁of ▁Kal ank atu yk , ▁where ▁they ▁were ▁either ▁s lain ▁or ▁taken ▁prisoner . ▁The ▁conquer ors ▁im posed ▁upon ▁Ag h van ia ▁a ▁heavy ▁system ▁of ▁tax