Despite their efforts, the emperors at Constantinople could not reconquer the West and thus reconstitute the Roman Empire of Augustus. Indeed, theological controversy, reflecting internal political strain, and combined with Persian and Arab aggression, cost the Empire Syria and Egypt. The internal structure was modified to meet the new situation.
From 717 to 867 the threat of Arab conquest was safely contained, the Bulgarians were converted, the major religious and political struggle over church images was fought and decided, and the large landowners began to emerge as a threat to the financial and military system.
From 867 to 1025 the Byzantine Empire was at its height. The emperors counterattacked the Arabs and regained much territory and prestige; the grim Bulgarian struggle was fought to a bloody conclusion; the Russians were converted; and the emperors made every effort to check the growth of the great landowning aristocracy. But the years 1025-1081 represented a period of decline, slow at first, accelerated as the period drew to a close.