In 476 AD the last of Rome's emperors was deposed by a barbarian general, the son of one of Attila the Hun's henchmen, and the imperial vestments were despatched to Constantinople. The curtain fell on the Roman Empire in Western Europe, its territories divided between successor kingdoms constructed around barbarian military manpower. But if the Roman Empire was dead, the dream of restoring it refused to die. In many parts of the old Empire, real Romans still lived, holding on to their lands, the values of their civilisation, its institutions; the barbarians were ready to reignite the imperial...