Constantine's successors, with frequently more than one Augustus dividing up the administration, were more or less constantly engaging in military efforts to protect the Empire and arrest what in hindsight was clearly a slow but steady decline in its fortunes. Valentian (364-375) and his brother Valens (364-378) split the administration of the Empire in two, with the elder and more capable Valentian taking western half. Unity was preserved in name until the death of their successor, Theodosius, in 395. One of his sons, Honorius, ruled the Western Roman Empire, while his other son, Areadius, ruled the Eastern Roman Empire.

SLOW AGONY

By the opening of the 5th century, anyone still under any illusion about the Empire's prospects must surely have seen the writing on the wall.

The Western Empire in particular careened quickly down the slippery slope. The main source of pressure came from wave after wave of barbarian invasions. Visigoths, Goths, Vandals, Burgundians, Franks and the fierce Attila's Huns all swept across Gaul, Spain, Italy and even into Africa. Saxons and other north German tribes poured into (by the mid-century) defenceless Britain. In 1476 the Germanic Odovacar proclaimed himself king in the Western Empire, a fait accompli tacitly accepted by the Eastern Empire. He was later trounced by the Ostrogoth Theodoric in 493, by which time the Western Empire had ceased to exist. Theodoric rules in Italy until 526.

The story in the Eastern Empire, with its capital in Constantinople, was rather different. Although also engaged in an interminable struggle for survival, its rulers managed to hold this half of the Empire together. By the time Justinian (518-565) came to the imperial throne, the map of the one time Roman world had changed beyond recognition. The Roman Empire (that is, what was left of its eastern half) stretched from parts of present-day Yugoslavia across to Bulgaria and Greece, Asia Minor, a deep strip of the Mediterranean coast of what is now Syria, Lebanon, Jordan and Israel ( facing the Persian Empire and free-wheeling Arab tribes) and down to Egypt and a strip of North Africa as far west as modern Libya.

In the west, Italy and much of what is now Yugoslavia was ruled by the Ostrogoths. Gaul was divided into the kingdoms of the Franks, Burgundians and Visigoths. The latter also controlled all of Iberia (modern Spain and Portugal). The Vandals exercised loose control over a long coastal strip of northern-western Africa. Roman and Romanised citizens rubbed along with their new bosses to a greater or lesser degree, in some cases managing to fill an important role as cultured and knowledgeable administrators of territories generally too vast for the newcomers to adequately populate or control alone.

Justinian, however, had a dream. He saw the glory of Rome restored and embarked on a series of wars of reconquest. At the height of his success he had retaken most of Italy (including Sicily, Sardinia and Corsica), extended imperial power in Africa to what is now north-western Algeria and even controlled a coastal slice of southern Spain. At the same time he codified Roman law and attempted to quash growing schismatic tendencies within the Christian church by favouring the western ( Roman) branch. It was all costly, and ultimately futile, exercise. As the early Middle Ages crept up on Europe, forces far beyond the control of Justinian and his Byzantine successors would forever seal the tomb in which lay the once mighty Roman Empire. Within three years of Justinian's death, the Lombard tribes lurking to the north of Italy launched invasions on the peninsula. The Byzantines were left with Ravenna and other pockets along the south-eastern coast of Italy.

Meanwhile in Rome, the western Church was asserting itself as a spiritual and secular force. Pope Leo L 'the Great' (440-461) had convinced Attila the Hun not to sack Rome, and Pope Gregory I (590-604) set the pattern of Church administration that was to guide Catholic services and rituals throughout history. Gregory oversaw the Christianisation of Britain and tightened relations with Church abroad ( mainly in Gaul and Spain), improved conditions for slaves, provided free bread in Rome and repaired Italy's extensive network of aqueducts. He also left an enormous volume of writing on which much Catholic dogma was subsequently based and he elevated the role of music in Catholic liturgy with the Gregorian chant.

LOMBARD ITALY & THE PAPAL STATES (600-800)

Even before Gregory became pope, the Lombard invasion of Italy had begun. The Lombards were a swabian people who appear to have originally inhabited the lower basin of the Elbe. As often happened with conquerors of the Italian peninsula, the Lombards ended up adopting much of the local culture, including language, rather than imposing their own. Their more communal concept of land and property tenure soon gave way to the Romans' high regard for private property, either absolute or leased, and the Lombards who settled mainly around Milan, Pavia and Brescia, soon became city-dwellers, building many churches and public baths that still grace these cities. They eventually expanded their control farther down the peninsula - taking over the important duchies of Spoleto and Benevento - although they were unable to take Rome.

In an effort to unseat the Lombards, the pope invited the Franks to invade Italy, which they duly did 754 and 756 under the command of the king, Pepin. The popes were, even at this early stage in the long history of the Church, an incredibly canny lot. The papacy invented the Donation of Constantine, a document in which the Roman emperor Constantine I purportedly granted the Church temporal control of the city of Rome and surrounding territories. At this point Rome was technically controlled by the duke of Rome, under the auspices of the Eastern Empire in Constantinpole. In return or the papal blessing and an ill-defined say in Roman affairs, Pepin marched into Italy, defeated the Lombards and at the same time declared the creation of the Papal States (i.e, territories under the direct political control of the pope), whose number and constitution would change constantly over the centuries. They survived until 1870. Using the Donation of Constantine as his precedent, Pepin issued the Donation of Pepin in 756, under which land still nominally belonging to the Byzantine Empire was awarded to Pope Stephen II.

When Pepin's son and successor, Charlemagne, visited Rome in 774, he confirmed the Donation of Pepin. Charlemagne was crowned emperor by Pope Leo III in St Peter's Basilica on Christmas Day 800 and the concept of the Holy Roman Empire came into being. The bond between the papacy and the Byzantine Empire was thus forever broken and political power in what had been the Western Roman Empire shifted north of the Alps, where it would remain for more than 1000 years. This early collaboration between papacy and Empire would later degenerate into enmity, and the cycle of papal-imperial conflict would mark the history of Italy for centuries to come.

Charlemagne's successors were unable to hold together his vast Carolingian Empire. In 843 the Partition of Verdun divided in between his three nephews, and Italy became a battleground of rival powers and states. The imperial crown was ruthlessly fought over, similarly Rome's aristocratic families engaged in battle for the papacy.

AN OASIS OF CALM

Meanwhile, momentous events were taking place on the south side of the Mediterranean. The rise on the early decades of the 7th century of a new monotheistic faith, Islam, among the Arab tribes under the guidance of the prophet Mohammed passed unnoticed in Europe. Upon the death of Mohammed in 632 the Muslims, as his followers were called, embarked on an astonishing campaign of conquest, in which they seemingly won the hearts and minds of many of the conquered, across the Middle East and all of North Africa. In 711 they crossed into Spain and their lightning advance was only brought to a halt in Poitiers, Western France in 732.

Given their spectacular progress in the west, it is surprising that the Muslims took so long to try their luck in Italy. The Aghlabid dynasty in Tunisia had launched repeated raids against nearby Sicily since the second half of the 7th century, but only in 827 did they make a serious landing. From then they embarked on a slow campaign of conquest, and one by one the Greek ( read Byzantine) cities of the island fell. Palermo went in 831. The last to surrender was Taormina in 902.

The Muslims ( who in Italy came to be known as Saracens), a mix of Arabs and Berbers, established a splendid civilisation. The fundamentals of Greek culture were restored and elaborated on by Muslim scholars such as the physician and philosopher Avicenna, the astronomer and geographer Al-Battani and the mathematician Al-Kovarizmi. Cotton, sugar cane, oranges and lemons were introduced in the south, taxes were lower than elsewhere in Italy and the Sicilian lived relatively peacefully under their Arab lords for more than two centuries.

The Muslims were soon on the mainland largely as mercenaries in the service of rival southern potentates, mostly Byzantine Greek in orientation if not always politically loyal or ties to Constantinpole. The Muslims gained a foothold for themselves, too, occupying Taranto and Bari.

Amalfi, which had secured independence from Naples in the 840's, soon became a major trading republic in the western Mediterranean. It also became a centre of great cosmopolitan civilisation and learning- as did the republics of Gaeta and Naples, and Salerno, which was still a Lobard principality. In the 11th century Salerno was famous for its medical school, where Greek, Jewish, Muslim and western Christian teachers worked together.