Two external forces served to shape the Middle Ages: the Byzantine Empire and Islam. More than merely defining the geographical borders of the medieval world, they interacted with it, producing, at times, friction and, at other times, great achievements. As much as any two individuals can effect movements and institutions containing their own inner dynamics, the emperor Justinian and the prophet Mohammed can be said to have shaped the Middle Ages by establishing contexts, limits and opposition to the European West. It was once said (by Henri Pirenne) that ‘without Mohammed Charlemagne would have been inconceivable’. Taking a broader view, it may be said that without Justinian and Mohammed there would never have been a Frederick II and Innocent III, i.e., there never would have been a medieval empire and a medieval papacy. It is a proposition worth examining.
Few perhaps expected it at the time, but Justinian (527-65) was the last in a centuries-long line of native Latin-speaking emperors. Although his uncle Justin (518-27) rose to the purple as a military commander, Justinian, Illyrian-born, was educated at Constantinople and played a substantial policy-making role in his uncle s reign. Among the most intellectual of Roman emperors and perhaps the hardest working, Justinian, judged in terms of his territorial aims, must be seen as a failure. His overarching aim was to preserve and perfect the Roman Empire, and, if preservation required restoration, so be it.
The territorial integrity of the traditional empire required Justinian to undertake the reconquest of the West from the German tribes that now ruled those imperial lands. It was a reconquest that was to prove expensive, partial and short-lived. Britain was recognized as lost for ever, but Justinian’s ambitions saw North Africa, Italy, Spain and perhaps even Gaul under his effective authority, with the Mediterranean once again an inland Roman sea. Twice his general, Belisarius, returned to Constantinople, bringing defeated German kings with him: the Vandal Gelimer (534) and the Ostrogoth Witgis (540). And when the dust raised by the imperial armies (always containing large numbers of