The most important illuminating source that survived from the two centuries termed "the dark ages of Byzantium" is the chronicle of the monk Theophanes (d. 817 or 818). In it Theophanes paints a vivid picture of the Empire's struggle in the seventh and eighth centuries both to withstand foreign invasions and to quell internal religious conflicts. Theophanes's carefully developed chronological scheme was mined extensively by later Byzantine and Western record keepers; his chronicle was used as a source of information as well as a stylistic model. It is for us the framework upon which all Byzantine chronology for this period must be based.