The decline of the Roman Empire as a political force after the sixth century is incontestable. During the 630s the state proved unable to repel or neutralize the unexpected challenge of the Arabs, who came from an area of the empire that had previously been both metaphorically and literally marginal and had never previously posed a major threat. The arguments in this chapter suggest that the central cause of this collapse was not exhaustion caused by the twenty-year struggle with the rival empire of the Sassanians, but an acute demographic – and therefore economic – recession caused by the plague across the regions of Europe, the Mediterranean, and the Near East. By the beginning of the seventh century Rome could neither summon nor deploy the resources necessary for sustained military or diplomatic efforts against determined enemies. The implosion of the Roman state as a viable world power had been matched by internal cultural and social changes. Throughout late antiquity the empire had been transformed by the changing role and nature of Christianity within Roman society, and the symptoms of this, all extensively discussed and analyzed in modern scholarship, were especially apparent in the sixth and early seventh centuries. They include the emergence of bishops as community leaders, who became dominant figures in secular as well as religious matters,71 and the growing importance of Christian asceticism, which underpinned the influence of charismatic individual saints,72 and even more importantly led to the creation of the monastic movement.73 In the east the sixth and early seventh centuries were marked by an abundance of church building, carried out during a period of demographic and economic recession, as well as new forms of popular religious activity, notably processions involving whole communities, which were designed to harness popular piety and secure divine favor and intercession in the face of crisis, natural disaster, or other threats to a community's well-being.74 This heightened religious sensibility, which changed the nature of Christianity itself, had also affected the running of the Roman state especially in the last century from Justinian to Heraclius. Christian and imperial ideology were self-consciously fused in the public rhetoric of Justinian's laws, and Justinian's own reign, especially his later years, present a new image of the emperor and the state entirely subservient to God's will.75 Rome's final confrontation with the Sassanians, especially during the apocalyptic Siege of Constantinople in 626, saw many strands of this new religious passion woven together: the city's defense organized by the patriarch Sergius; the invocation of the holy relic of the Virgin's Rome as a talisman to save the city; collective prayers and processions as a means to secure divine protection; and the casting of the war with the Sassanians as a crusade against a religious enemy (see pp. 455–8).
As always in the history of the later Roman Empire, it is easy to be impressed and overwhelmed by the quantity of evidence for the impact and influence of Christianity on society and culture at all levels. This impression is, of course, partly a consequence of the ubiquity and eloquence of Christian sources, which drown out other voices. However, not all Roman secular institutions vanished with the fall of the empire. Roman systems of taxation survived the collapse of empire and were revived by subsequent regimes whenever these had the capacity to administer and enforce them. Roman law formed the basis for the law codes of the successor kingdoms in the west, although it was largely superseded by Islamic Sharia law in the east. Latin, the official language of the western empire, which had established itself as the vernacular speech of the Mediterranean provinces, gradually evolved into the Romance languages of southern Europe, although Germanic and Slavic languages prevailed in the northern regions of the western empire, and Arabic spread through north Africa in the wake of the Arab conquests. Greek, meanwhile, also made way for Arabic in the Near East, and much later after the fall of the Byzantine Empire, for Turkish in most of Asia Minor. Both Latin and Greek, however, survived as the languages of the western and eastern Church respectively. The literate inhabitants of western monasteries, by copying examples of classical literature, ensured the preservation and transmission of Greek and Roman literary culture to the later middle ages, a tradition that was well under way in the sixth century. They also ensured that Latin would become the intellectual language of the Renaissance and early modern Europe. In the east, by contrast, classical culture survived and was transmitted through translation into Arabic, especially on the initiative of the Abbasid Muslim caliphate based in Baghdad from the later eighth century. Whereas the classical traditions of the western Roman Empire formed a cultural heritage that palpably shaped the outlook of Renaissance Europe, the afterlife of the eastern empire was less tangible. Although the eastern Orthodox Church preserved a continuous tradition of eastern, Greek-speaking Christianity, the secular achievements and legacy of the Greek Roman Empire of the East have largely been a matter for rediscovery by western scholars since the enlightenment. Our view not only of Rome's decline and fall, but of the history of its empire in the west and in the east as a conceptual and intellectual unity, still owes an enormous debt to the mighty narrative of Gibbon.