▁been ▁argued ▁that ▁Char lemagne ▁was ▁an ▁indirect ▁product ▁of ▁Muhammad : ▁" The ▁Frank ish ▁Empire ▁would ▁probably ▁never ▁have ▁existed ▁without ▁Islam , ▁and ▁Char lemagne ▁without ▁Mah omet ▁would ▁be ▁incon ce iv able ." ▁ ▁The ▁Holy ▁Roman ▁Empire ▁of ▁Char lemagne ' s ▁success ors ▁would ▁later ▁come ▁to ▁the ▁aid ▁of ▁the ▁By z ant ines ▁under ▁Louis ▁II ▁and ▁during ▁the ▁Cr us ades , ▁but ▁relations ▁between ▁the ▁two ▁emp ires ▁would ▁be ▁stra ined ; ▁based ▁on ▁the ▁Sal erno ▁Chron icle , ▁we ▁know ▁the ▁Emperor ▁Bas il ▁had ▁sent ▁an ▁angry ▁letter ▁to ▁his ▁western ▁counter part , ▁repr im and ing ▁him ▁for ▁us ur ping ▁the ▁title ▁of ▁em peror . ▁He ▁argued ▁that ▁the ▁Frank ish ▁r ul ers ▁were ▁simple ▁reg es , ▁and ▁that ▁each ▁nation ▁has ▁its ▁own ▁title ▁for ▁the ▁r uler , ▁whereas ▁the ▁imperial ▁title ▁su ited ▁only ▁the ▁r uler ▁of ▁the ▁Eastern ▁Rom ans , ▁Bas il ▁himself . ▁ ▁Histor i ography ▁and ▁other ▁sources ▁ ▁Walter ▁Emil ▁Ka eg i ▁states ▁that ▁ext ant ▁Arab ic ▁sources ▁have ▁been ▁given ▁much ▁scholar ly ▁attention ▁for ▁issues ▁of ▁obsc ur ities ▁and ▁contradict ions . ▁However , ▁he ▁points ▁out ▁that ▁By z antine ▁sources ▁are ▁also ▁problem atic , ▁such ▁as ▁the ▁chron icles ▁of ▁The oph anes ▁and ▁Nice ph orus ▁and ▁those ▁written ▁in ▁Sy ri ac , ▁which ▁are ▁short ▁and ▁ter se ▁while ▁the ▁important