Repercussions

Justinian's wars restored Roman rule over Africa, Italy, and part of Spain, briefly making the Mediterranean a Roman lake once more. But the reconquest was overextended and underfunded, and it did not last — the Lombards seized most of Italy within fifteen years of his death, and the western holdings were steadily lost thereafter. The failure of the restoration confirmed the permanent division of the Mediterranean world and the end of a unified Roman empire, even as it left the Eastern (Byzantine) Empire exhausted for the struggles to come.

The eighteen-year Gothic War, with its repeated sieges, famines, and sackings — compounded by the Plague of Justinian — devastated Italy, collapsing its population, its economy, and the civic institutions of the ancient world. Rome shrank from a great metropolis to a village among ruins. The war did more than the earlier barbarian invasions to end classical civilisation in Italy, hastening the transition from the ancient world to the early Middle Ages and leaving a shattered land for the Lombards and the papacy to inherit.

Alongside the wars, Justinian ordered the codification of a thousand years of Roman law into the Corpus Juris Civilis — the Code, Digest, Institutes, and Novels. It preserved and systematised Roman legal thought as no other project had. Rediscovered in the medieval West, the Corpus became the foundation of the civil-law tradition taught in Europe's universities and underlying the legal systems of most of continental Europe, Latin America, and beyond to this day.

In 541–542, the first recorded pandemic of bubonic plague swept the empire, killing perhaps a quarter to a half of its population in waves that recurred for two centuries. It gutted the armies and tax revenues at the height of the reconquest and crippled the empire's capacity to hold its gains. The plague permanently weakened the Eastern Empire, is thought by many historians to have helped end antiquity and clear the way for the later Islamic conquests, and stands as one of the deadliest pandemics in human history.

The cost of the western wars, in men and treasure, left the Eastern Empire drained and its eastern and Balkan frontiers dangerously stripped. The overstretch contributed to renewed disaster on the Persian frontier and to the inability to resist the Slavs, Avars, and later the Arabs. Justinian's overextension is often seen as a strategic blunder that weakened Byzantium for the catastrophic wars of the seventh century — the Byzantine–Sasanian War and the Islamic conquests — that would strip away half the empire.

Justinian rebuilt Constantinople after the Nika Riots on a monumental scale, crowned by the great domed church of Hagia Sophia — an engineering marvel and the largest cathedral in the world for nearly a thousand years — along with fortifications and churches across the empire. Hagia Sophia became the supreme masterpiece of Byzantine architecture and a model for church and mosque builders for over a millennium; it still stands in Istanbul as one of the world's most influential buildings.

The reconquest gave the empire the wealthy province of Africa, which it held for over 150 years until the Arab conquest, and the exarchate of Ravenna in Italy, a Byzantine foothold that endured for two centuries and shaped the emergence of the medieval papacy and the Italian political landscape. Byzantine Ravenna and its exarchate preserved a Roman presence in Italy that influenced the rise of papal power and left a legacy of stunning mosaics; Byzantine Africa remained a rich imperial province until 698.

Belisarius's celebration in 534, with the captured Vandal king and treasure paraded through Constantinople, was the last triumph in the thousand-year Roman tradition, and his and Narses's campaigns were the last great victories won in the classical Roman manner. The end of the triumph symbolised the passing of the ancient Roman military and political world into its Byzantine and medieval successors, marking Justinian's age as a threshold between antiquity and the Middle Ages.

The story of Belisarius — the empire's greatest general, repeatedly distrusted and under-supported by an ungrateful emperor, and (in later, probably false, legend) reduced to a blind beggar in his old age — became one of history's enduring parables of unrewarded loyalty and the ingratitude of rulers. The Belisarius legend inspired paintings, novels, and operas for centuries, from Jacques-Louis David to modern historical fiction, keeping the memory of Justinian's wars alive in Western culture.