The Emperor Justinian survived his greatest general by a mere eight months and the conquests undertaken during his reign did not hold. Under his successors, North Africa fell to Islam and they, crossing the Straits of Gibraltar, took most of Spain as well. Between Rome and the Alps, despite the success of Narses and his huge army, a level of force never granted to Belisarius, it remained an area of conflict between Franks, Burgundians and Lombards until it became part of Charlemagne’s Holy Roman Empire.
Only in the south did the conquests hold. Byzantium continued to rule the lower half of Italy, despite Saracen and Lombard pressure, for five centuries. The race that subdued the Lombards and finally evicted from Italy a polity that still thought of itself as the Roman Empire, were the Normans, a story told by the author in a trilogy beginning with Mercenaries.