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 the framework upon which all Byzantine chronology for this period must be based. Important topics covered by the Chronicle include: The Empire's struggle to repel explosive Arab expansionism and the Bulgar invasion. The iconoclastic controversy, which caused civil war within Byzantium and led to schism between the churches of Constantinople and Rome. The development of the Byzantine thematic system, the administrative and social structure that would bring the Empire to the height of its power and prosperity. Almost all the sources used by Theophanes have perished, leaving his chronicle as the most important historical literature from this period. Turledove's translation makes available in English this crucial primary text for the study of medieval Byzantine civilization.