Roman Empire.  
Eastern Roman (Byzantine) restoration.  
In 480, the last claimant to the title of Western Roman emperor, Julius Nepos, was murdered and a Roman general of barbarian origin, Odoacer, declared allegiance to Eastern Roman emperor Zeno. Despite owing nominal allegiance to Constantinople, Odoacer and later the Ostrogoths continued, like the last emperors, to rule Italy as a virtually independent realm from Ravenna. Meanwhile, the Senate, even though long since stripped of wider powers, continued to administer Rome itself, with the Pope usually coming from a senatorial family. This situation continued until Theodahad murdered Amalasuntha, a pro-imperial Gothic queen, and usurped the power in 535. The Eastern Roman emperor, Justinian I (reigned 527–565), used this as a pretext to send forces to Italy under his famed general Belisarius, recapturing the city next year, on 9 December AD 536. In 537–538, the Eastern Romans successfully defended the city in a year-long siege against the Ostrogothic army, and eventually took Ravenna, too.  
Gothic resistance revived however, and on 17 December 546, the Ostrogoths under Totila recaptured and sacked Rome. Belisarius soon recovered the city, but the Ostrogoths retook it in 549. Belisarius was replaced by Narses, who captured Rome from the Ostrogoths for good in 552, ending the so-called Gothic Wars which had devastated much of Italy. The continual war around Rome in the 530s and 540s left it in a state of total disrepair – near-abandoned and desolate with much of its lower-lying parts turned into unhealthy marshes as the drainage systems were neglected and the Tiber's embankments fell into disrepair in the course of the latter half of the 6th century. Here, malaria developed. The aqueducts, except for one, were not repaired. The population, without imports of grain and oil from Sicily, shrank to less than 50,000 concentrated near the Tiber and around the Campus Martius, abandoning those districts without water supply. There is a legend, significant though untrue, that there was a moment where no one remained living in Rome.  
Justinian I provided grants for the maintenance of public buildings, aqueducts and bridges—though, being mostly drawn from an Italy dramatically impoverished by the recent wars, these were not always sufficient. He also styled himself the patron of its remaining scholars, orators, physicians and lawyers in the stated hope that eventually more youths would seek a better education. After the wars, the Senate was theoretically restored, but under the supervision of the urban prefect and other officials appointed by, and responsible to, the Eastern Roman authorities in Ravenna.  
However, the Pope was now one of the leading religious figures in the entire Byzantine Roman Empire and effectively more powerful locally than either the remaining senators or local Eastern Roman (Byzantine) officials. In practice, local power in Rome devolved to the Pope and, over the next few decades, both much of the remaining possessions of the senatorial aristocracy and the local Byzantine Roman administration in Rome were absorbed by the Church.
The reign of Justinian's nephew and successor Justin II (reigned 565–578) was marked from the Italian point of view by the invasion of the Lombards under Alboin (568). In capturing the regions of Benevento, Lombardy, Piedmont, Spoleto and Tuscany, the invaders effectively restricted Imperial authority to small islands of land surrounding a number of coastal cities, including Ravenna, Naples, Rome and the area of the future Venice. The one inland city continuing under Eastern Roman control was Perugia, which provided a repeatedly threatened overland link between Rome and Ravenna. In 578 and again in 580, the Senate, in some of its last recorded acts, had to ask for the support of Tiberius II Constantine (reigned 578–582) against the approaching Dukes, Faroald I of Spoleto and Zotto of Benevento.  
Maurice (reigned 582–602) added a new factor in the continuing conflict by creating an alliance with Childebert II of Austrasia (reigned 575–595). The armies of the Frankish King invaded the Lombard territories in 584, 585, 588 and 590. Rome had suffered badly from a disastrous flood of the Tiber in 589, described by Paul the Deacon as a "swarm of snakes." This was followed by a plague in 590, which was notable for the legend of the angel seen, while the newly elected Pope Gregory I (term 590–604) was passing in procession by Hadrian's Tomb, to hover over the building and to sheathe his flaming sword as a sign that the pestilence was about to cease. The city was safe from capture at least.  
Agilulf, however, the new Lombard King (reigned 591 to c. 616), managed to secure peace with Childebert, reorganised his territories and resumed activities against both Naples and Rome by 592. With the Emperor preoccupied with wars in the eastern borders and the various succeeding Exarchs unable to secure Rome from invasion, Gregory took personal initiative in starting negotiations for a peace treaty. This was completed in the autumn of 598—later recognised by Maurice—lasting until the end of his reign.  
The position of the Bishop of Rome was further strengthened under the usurper Phocas (reigned 602–610). Phocas recognised his primacy over that of the Patriarch of Constantinople and even decreed Pope Boniface III (607) to be "the head of all the Churches". Phocas's reign saw the erection of the last imperial monument in the Roman Forum, the column bearing his name. He also gave the Pope the Pantheon, at the time closed for centuries, and thus probably saved it from destruction.  
During the 7th century, an influx of both Byzantine Roman officials and churchmen from elsewhere in the empire made both the local lay aristocracy and Church leadership largely Greek speaking. The population of Rome, a magnet for pilgrims, may have increased to 90,000.[62] Eleven of thirteen popes between 678 and 752 were of Greek or Syrian descent. However, the strong Byzantine Roman cultural influence did not always lead to political harmony between Rome and Constantinople. In the controversy over Monothelitism, popes found themselves under severe pressure (sometimes amounting to physical force) when they failed to keep in step with Constantinople's shifting theological positions. In 653, Pope Martin I was deported to Constantinople and, after a show trial, exiled to the Crimea, where he died.  
Then, in 663, Rome had its first imperial visit for two centuries, by Constans II—its worst disaster since the Gothic Wars when the Emperor proceeded to strip Rome of metal, including that from buildings and statues, to provide armament materials for use against the Saracens. However, for the next half century, despite further tensions, Rome and the Papacy continued to prefer continued Byzantine Roman rule: in part because the alternative was Lombard rule, and in part because Rome's food was largely coming from Papal estates elsewhere in the Empire, particularly Sicily.

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