▁question ▁of ▁their ▁sources ▁and ▁their ▁use ▁of ▁sources ▁remains ▁un resol ved . ▁Ka eg i ▁con cludes ▁that ▁sch ol ars ▁must ▁also ▁subject ▁the ▁By z antine ▁tradition ▁to ▁critical ▁scr ut iny , ▁as ▁it ▁" contains ▁bias ▁and ▁cannot ▁serve ▁as ▁an ▁objective ▁standard ▁against ▁which ▁all ▁Muslim ▁sources ▁may ▁be ▁confident ly ▁checked ". ▁ ▁Among ▁the ▁few ▁Latin ▁sources ▁of ▁interest ▁are ▁the ▁ 7 th - century ▁history ▁of ▁Fre deg arius , ▁and ▁two ▁ 8 th - century ▁Spanish ▁chron icles , ▁all ▁of ▁which ▁draw ▁on ▁some ▁By z antine ▁and ▁orient al ▁historical ▁trad itions . ▁As ▁far ▁as ▁By z antine ▁military ▁action ▁against ▁the ▁initial ▁Muslim ▁invas ions , ▁Ka eg i ▁as ser ts ▁that ▁" By z antine ▁trad itions ▁... ▁attempt ▁to ▁def lect ▁criticism ▁of ▁the ▁By z antine ▁deb acle ▁from ▁Her ac lius ▁to ▁other ▁persons , ▁groups , ▁and ▁things ". ▁ ▁The ▁range ▁of ▁non - histor ical ▁By z antine ▁sources ▁is ▁vast : ▁they ▁range ▁from ▁pap y ri ▁to ▁ser m ons ▁( most ▁notable ▁those ▁of ▁S op hr on ius ▁and ▁An ast as ius ▁S ina ita ), ▁poetry ▁( es pecially ▁that ▁of ▁S op hr on ius ▁and ▁George ▁of ▁P is idia ) ▁including ▁the ▁Ac rit ic ▁songs , ▁correspond ence ▁often ▁of ▁a ▁pat rist ic ▁proven ance , ▁apolog et ical ▁treat ises , ▁ap oc aly ps es