The Italian peninsula lay in the western half of the Roman Empire after its division in the late 3rd century and its permanent separation in 395. In the late 480s the Ostrogoths, with the sanction of the Emperor in the East, attacked the general who was ruling Italy and overthrew him after several years, but any hopes the Byzantine Emperor still had that this would bring Italy back into the Empire were disappointed.
In 533-4 the Byzantine Empire overthrew the Vandal Kingdom in northwest Africa and the western Mediterranean islands, and in 535 the Byzantine armies crossed to Sicily, whose western tip was Vandal but which was mainly Ostrogothic, and captured the island. The mainland of Italy was invaded in 536 and conquered by the end of the decade, but in the 540s the Ostrogoths revived under a new King, Totila, and a new, prolonged and destructive war followed. Only in 555 was the Byzantine victory secure, and even then there were pockets of resistance. Brescia and Verona did not surrender until 563.
Scarcely had the Imperial adminstration begun the task of restoring the prosperity of Italy than the Lombards, a Germanic confederation of tribes, invaded from the northeast in 568. The lands of the Po plain fell to them, so did Tuscany. In east central Italy by the end of the century the Lombards had established a Duchy centred on Spoleto and another in the south of the peninsula centred on Benevento. At the beginning of the 7th century the Byzantine Empire was left with Liguria, the lagoons of the northern Adriatic, an extensive central strip of land running southwestwards from Ravenna through Umbria to Rome, districts on the Tyrrhenian coast north and south of Naples, the heel and toe of Italy, and the island of Sicily.
The chief official in Byzantine Italy was the Exarch (the first surviving record of the title comes from 584). He combined the leadership of both the military and civil administrations, thus breaking the pattern of late Roman provincial administration, where the two were placed under separate officers.
The Lombards took Liguria in 643, in the south they pushed the Byzantines back into the toe and heel of Italy, and in 751 they took the lands of central Italy, including Ravenna, but not the Venetian lagoon and not Rome and its environs. The Exarchs had allowed considerable autonomy to Rome and to its Bishop; the Pope had taken part in negotiations with the Lombards and the Papacy was emerging as a temporal power.
Byzantine Italy was further reduced when the Aghlabids, the Moslem rulers in the Tunisia region, began the invasion of Sicily in 827. The west and centre of the island soon fell, but it was not until 878 that Syracuse, the last great city on the east coast, was taken, and not until 902 that the last fortress, at Taormina, surrendered. The Arabs also drove the Byzantines out of the heel of Italy in the 840s. They were expelled from Bari by the western Emperor, Louis II, in 871, but he ran into trouble with the Lombards and died in 875. By 888 a resurgent Byzantium had taken control of much of southern Italy from both the Arabs and the Lombards. Besides always keeping at least a toehold on Italy, the Byzantines had retained influence over the ports on the western coast at Naples, Amalfi and Gaeta. When central Italy was lost, these cities were remote from the Byzantine authorities in the south and became self-governing.
In 1038 the Byzantines began the reconquest of Sicily from the Moslems and made spectacular gains in the east of the island, but the commander was recalled in 1040 and the Arabs soon recovered their losses, except for Messina. On the mainland the Lombards put pressure on the Byzantines, though a savage campaign in 1042-3 restored Byzantine authority. By that period there was a new presence in the south of Italy: Norman mercenaries had been fighting for several years for one side or the other. Some of them were already beginning to act on their own account and in the next thirty years they steadily expanded the area they controlled. In 1071, the same year as Romanus IV was defeated by the Seljuk Turks at Manzikert, the Normans captured Bari, the capital of Byzantine Italy and its last remaining stronghold.
There was a brief return. In 1155, with Roger II, the founder of the Sicilian Kingdom, dead, and his son William I ill, a Byzantine force attacked Apulia. The city of Bari, where many Greeks still lived, welcomed the invaders; Brindisi and Taranto were also taken, but in the following year William I defeated the Byzantines and recovered Apulia. Further north the city of Ancona, once part of the Exarch’s territory and within territory claimed by both the Pope and the Holy Roman Emperor, allied itself with Byzantium in 1155. The alliance survived until the death of the Emperor Manuel in 1180. When this alliance ended the Empire that still called itself Roman ceased to hold any part of Italy.