From 535 to 554, the Romans under the Emperor Justinian gradually reconquered Italy from the Ostrogoths. The conflict utterly devastated the peninsula and seriously weakened the Roman economy, with the result that for decades to come the empire lay helpless and vulnerable.
The Lombards, who are said to have originated in Scandinavia, had over decades migrated south through Germania until they reached the frontier of the empire. In 568 they stormed into Italy, overwhelmed the small Roman army that was all the empire could afford to guard the region, and founded their own kingdom in the ruins. A few areas, including Liguria, Latium, the Pentapolis, Apulia and Calabria, remained under Roman control, but the rest became Langobardia.
In 584 the remaining Roman territories were reorganized into the Exarchate of Italy, a grouping of provinces with considerable autonomy over military and diplomatic matters. The Exarch, based in Ravenna, and the Pope of Rome were often at loggerheads with each other, but when they cooperated they could together be a powerful force to oppose the Lombards.
In 633 the Emperor Heraclius summoned the Third Council of Constantinople, an ecumenical council of the Church, to discuss the orthodoxy or heterodoxy of the new creed of Islam. The Arian Lombard bishops supported the Emperor's stance and helped him override the fierce opposition posed by the bishops of Roman Greece and Italy, thus permanently damaging the relations between Ravenna and Constantinople. When Heraclius looked about to win the resulting civil war between the Chalcedonian and Muslim factions, Exarch Isaac, with the support of the Pope, proclaimed in 637 the restoration of the Western Roman Empire, independent from Heraclius and the east.
Suddenly able to take control of his own destiny, Emperor Isaac raised taxes, strengthened the army using reinforcements from Africa and Mauritania, and set out to punish the Lombards for their perceived betrayal of Christianity. By 640 he had overcome all resistance, and defeated and killed their last king Rothari in June of that year.
Some of the surviving Lombards fled north or west, while others remained and were gradually assimilated into West Roman society. Never again would a Lombard state rise again to its former power.