During the 600s, there was disagreement between Rome and Constantinople on religious matters. Pope Martin I was deported to Constantinople in 653, put on trial, and exiled. Emperor Constans II visited Rome in 663. The was the first Imperial visit to the city in 200 years. In 727, Pope Gregory II organized an iconoclasm, the destruction of icons and other religious symbols. Emperor Leo III failed to enforce his decrees and sent troops, but the attack was unsuccessful. In 731, the Emperor confiscated the pope’s estates in Calabria and Sicily, transferring them to the Patriarch of Constantinople, the counterpart of the Roman Pope. This had the effect of the expulsion of Rome from the Byzantine Empire. At this time, the Lombards, who were experiencing a revival, invaded and razed the Roman countryside. There was little the pope could do against the Lombards, who had become allies of Byzantium. Pope Gregory III asked the Franks for help. Lombard’s king, Aistulf, conquered Ravenna and Ferrara and set his sights on Rome. Pope Stephen II reacted by naming King Peppin of the Franks as Protector of Rome. Later that year, the king and the pope defeated Aistulf at Susa. In 756, Aistulf laid Rome under siege. When the Lombards heard Peppin was approaching, they fled to the north. The Papal States were formed after Peppin donated some lands to the pope.

The next king of the Lombards, Desiderius, plotted to capture Rome and seize the pope in 771. The plot failed. The pope defeated Desiderius with the support of Charlemagne in 773. This was the end of the Lombard Kingdom.