Origins of the empire and sources of imperial ideas
There was no inherent reason why, after the fall of the Roman Empire in the West in 476 and the establishment there of Germanic kingdoms, there should ever again have been an empire, still less a Roman empire, in western Europe. The reason this took place is to be sought (1) in certain local events in Rome in the years and months immediately preceding Charlemagne’s coronation in 800, and (2) in certain long-standing tendencies that made this particular solution of a difficult situation thinkable. These long-standing tendencies are to be regarded as preconditions rather than causes of the coronation; they do not account for it, but without them it is difficult to imagine how it could have taken place.
The first is the persistence, despite the fact that it was no longer a political reality west of Italy, of the idea of the universal and eternal Roman Empire. The importance of this tradition may easily be exaggerated. After the establishment of the Germanic kingdoms, kings such as Clovis in Gaul and Theodoric the Great in Italy were glad to accept Roman titles from the Byzantine emperor, who sought to maintain the formal unity of the Roman Empire by treating them as his vicars and lieutenants; but this was a short-lived expedient. By the 8th century any sense of belonging to the empire, by then confined to eastern Europe, had disappeared in the West.
Religious origins
Far more effective in the minds of the barbarian peoples of the West was the idea of the Imperium Christianum, or “Christian Empire,” which took shape after the conversion of Constantine the Great and the reconciliation between Christianity and the Roman Empire. Not only did the Christian church become a state church, including in its liturgy prayers for the empire and the emperor, but it also brought the Roman Empire into the framework of Christian eschatology (doctrine of last things), as the last of the world monarchies whose end would mark the inception of the kingdom of God. Through Christian iconography and through the liturgy the church’s view of the empire as a vehicle of God’s will, for the Christianization of the world, became prevalent. It was expressed with peculiar force in the letters of Charlemagne’s adviser Alcuin.
Apart from the persistence of the idea of a Christian Roman Empire, a third precondition for the establishment of an empire in the West was the existence of a candidate of sufficient power and standing in the person of the Frankish king. The Frankish kingdom expanded until it comprised most of western Europe, and it acquired the Lombard kingdom in northern Italy in 774. The importance of the ties forged by Charlemagne’s immediate predecessors with the papacy are obvious. Though it is scarcely true that Charlemagne’s accession to the empire was simply a consequence of this expansion, his outstanding position was evidently a precondition of his elevation to the imperial throne.
Political origins
When one turns from the preconditions to the causes of the events of 800 and from the realm of ideas to that of political facts, one enters another world. It is the world of the Byzantine (or Eastern) Empire, of which the pope was a subject, confirmed in his bishopric like other bishops by the Byzantine emperor. By the 8th century, however, the imperial position in Italy, centred in the Exarchate of Ravenna, was crumbling. Confronted by the power of Islam, the empire concentrated on the problems of the East and was unable to defend its Italian lands from the Lombards, who had entered Italy in 568. Furthermore, the Byzantine emperors of the Isaurian dynasty, of whom the first was Leo III (717–741), were estranged from the papacy by the Iconoclastic Controversy. Hitherto fear of the Lombards had kept the popes faithful to the Byzantine emperor and to the exarch in Ravenna, but the situation changed. When the Lombards renewed their advance southward, taking Ravenna in 751 and driving out the exarch, the pope appealed in vain to the Byzantine emperor. He then, in an epoch-making turn to the West, sought assistance from the Frankish king Pippin III the Short, who invaded Italy and reduced the Lombard king Aistulf to submission (754). Returning in 756, Pippin bestowed on the papacy the territories belonging to the exarchate. Thus was born both the temporal power of the papacy and the close alliance between the papacy and the Frankish monarchy.
Particularly significant of the anomalous position that had arisen in Italy was the action of the pope in conferring on the Frankish king the title of patrician, which could legally be conferred only by the emperor; in the form the pope gave it (patricius Romanorum), the title was meant to authorize its possessor to defend and support the Holy See against its foes. Even so, the papacy was reluctant to break its constitutional links with the imperial system, and this was particularly so under Pope Adrian I (772–795), after Charlemagne had in 774 defeated the last independent Lombard king, Desiderius, and taken his kingdom. As king of Lombardy the defender might become as dangerous to the pope as those against whom he had provided defense.
The events briefly related show, first, the growing estrangement between East and West; second, the difficult position of the pope between the Byzantine emperor and the Frankish king; third, the tenuousness of the imperial hold over Rome and central Italy. After the expulsion of the exarch in 751, the pope himself, in de facto possession, probably hoped to become the emperor’s successor in the West. Whether the document itself belongs to the 750s or not, this was the sense of the forged Donation of Constantine, in which the emperor Constantine I is represented as having conferred on Pope Sylvester I the imperial palace of the Lateran, the imperial insignia, and “all the provinces, places and cities of Italy and the western regions.” Such ambitions, however, proved illusory when Charlemagne became king of the Lombards. When it was even rumoured that Charles intended to depose Adrian and set up a Frankish pope in his place, it would have been folly for the pope to think of formal severance from the existing empire. Nevertheless, the empire’s shadowy titles were unlikely to be respected long in Italy unless the Byzantine emperor took action. From 781 papal documents were no longer being dated by the emperor’s regnal year, and the pope was minting his own coins.