The seventh century was a time of fundamental transformation throughout the eastern Mediterranean and Balkan world; and the most powerful political entity in that world experienced a succession of major upheavals. Entering the seventh century as the dominant political formation, stretching from Spain to the Euphrates and from the Danube to the Atlas mountains, it had been reduced by the end of our period – the year of the accession of Leo III in A.D. 717 – to a rump of its former self: East Roman rule in Egypt and North Africa, in Syria, Iraq and in eastern Anatolia had been swept away by the conquests of Islam, the new and vigorous world religion which was to provide the biggest threat to Christianity for the next thousand years. In the Balkans, Slavs and Bulgars had reduced Roman-controlled territory over the same period to the coastal areas and a few fortified settlements; while in Italy, the exarchate which had been established under Tiberius Constantine on the foundations of Justinian's reconquest was by the reign of Leo III all but extinguished. At the same time, new and powerful foes replaced older, traditional enemies: the expansion and the power of the caliphate centred at Damascus radically altered the balance of power in that area; in the Balkans, the establishment and consolidation of the Bulgar khanate posed a constant threat to Constantinople itself; while in the West, the increasingly independent see of St Peter was compelled to loosen its ties with Constantinople in order to preserve its own position as both leader of the Western Church and defender of its immediate hinterland.