 Although al @-@ Mu 'tasim 's reign was a time of peace in the Caliphate 's heartland territories , al @-@ Mu 'tasim himself was an energetic campaigner , and " acquired the reputation of being one of the warrior @-@ caliphs of Islam " . With the exception of the Amorium campaign , most of the military expeditions of al @-@ Mu 'tasim 's reign were domestic , directed against rebels and areas that , although nominally part of the Caliphate , had remained outside effective Muslim rule and where native peoples and princes retained de facto autonomy . 
