▁century ▁until ▁peace ▁was ▁made ▁with ▁the ▁S ass an ids . ▁After ▁the ▁Islam ic ▁Con quest ▁of ▁Iran , ▁Arab ▁inv aders ▁converted ▁most ▁of ▁its ▁people ▁to ▁Islam ▁and ▁made ▁it ▁part ▁of ▁the ▁cal i ph ate . ▁ ▁Islam ic ▁period ▁ ▁S as an ian ▁and ▁early ▁Islam ic ▁period ▁During ▁the ▁Arab ▁invasion ▁of ▁Iran , ▁the ▁Sp ah bed ▁of ▁Iran ▁was ▁Rost am ▁Far ro kh z ad , ▁the ▁son ▁of ▁Far ru kh ▁H orm iz d , ▁who ▁was ▁the ▁son ▁of ▁V ind uy ih , ▁the ▁uncle ▁of ▁Kh os ra u ▁I ▁and ▁brother ▁of ▁the ▁S as an ian ▁us ur per ▁V ist ah m . ▁R ust am ▁himself ▁was ▁born ▁in ▁A zer ba ij an ▁and ▁led ▁the ▁S as an ian ▁army ▁into ▁battle . ▁He ▁is ▁also ▁mentioned ▁in ▁the ▁Shah name h . ▁ ▁The ▁S as an ian ▁army ▁was ▁defeated ▁at ▁the ▁battle ▁of ▁al - Q ā dis i yy ah ▁and ▁Rost am ▁Far ro kh z ad , ▁along ▁with ▁many ▁other ▁S as an ian ▁veter ans , ▁was ▁killed . ▁In ▁ 6 4 2 , ▁Pir uz ▁Kh os row , ▁one ▁of ▁the ▁S as an ian ▁surv iv ors ▁during ▁the ▁battle ▁of ▁al - Q ā dis i yy ah , ▁fought ▁against ▁the ▁Muslim s ▁at ▁N ah av and , ▁which ▁was ▁a ▁gateway ▁to ▁the ▁provinces