In the early eighth century, the Byzantine emperors’ flirtation with Iconoclasm (rejecting the religious efficacy of images, icons, etc.) and their inability to protect Rome and the pope from the Lombard rulers of northern Italy persuaded Popes Gregory III (731–41), Zacharias (741–52) and Stephen II (752–7) to enter into alliances with the Franks, the rulers of a large kingdom that stretched from modern south-west France to the Rhineland and the Low Countries. As part of this new orientation of policy, the papal court (or Curia) concocted the so-called Donation of Constantine, one of the most powerful forgeries in world history only properly exposed in the fifteenth century. This claimed that, on becoming a Christian, the Emperor Constantine surrendered his imperial authority to Pope Sylvester I (314–35), who returned it while retaining pre-eminence over the other patriarchates, theoretical temporal jurisdiction over the western empire and direct rule of Rome, its surrounding region and Italy in general. This forgery formed one basis for the later papal insistence on its claims to a state in central Italy and its wider assertion of primacy over imperial authority in western Europe.
The papal–Frankish alliance proved mutually advantageous. The papacy gained effective protection in Italy; the Franks legitimacy for their mid- to late-eighth-century conquests in Lombardy, Gascony, Bavaria and Saxony between the Rhine and Elbe. The culmination of the alliance came on Christmas Day 800 when Pope Leo III (795–816) crowned the king of the Franks, Charles the Great or Charlemagne (768–814), as the new Roman emperor in the west, inaugurating what came to be known as the Holy Roman Empire, which survived, with various interruptions and changes of fortune, nature and substance, until abolished in 1806 on the insistence of Napoleon. While the Frankish, or Carolingian (i.e. family of Charles), empire lasted, until the 880s, the papacy remained rather overshadowed. Thereafter the throne of St Peter tended to be the preserve of a dim succession of Roman nobles, some youthful, dissolute, even irreligious. Yet the reputation of their office remained high, especially in northern Europe, where papal authority still appeared as a final arbiter of ecclesiastical and spiritual issues; the newly converted King Miesco I of Poland sought papal protection in 991. In 962, the king of Germany, Otto I, who had recently conquered northern Italy, revived the western empire by being crowned in Rome by Pope John XII (955–64), a notoriously debauched twenty-five-year-old nobleman and libertine who apparently met his death, still only about twenty-seven, after a stroke suffered during intercourse with a married woman.
By the early eleventh century the papacy alternated between grand protégés of the German emperors, such as the scholar Gerbert (Pope Sylvester II, 999–1003), and a succession of local appointees of distinctly uneven calibre usually taking the names Benedict or John. Increasingly elements within the Roman church and elsewhere in Christendom sought to reform both the papacy and the wider secular church in the west by re-emphasizing the separation and dominance of the spiritual over the secular in church appointments, management, finance and behaviour. Under the patronage of Emperor Henry III (1039–56), the reformers seized control of the papacy. A succession of German, Italian and French popes in the half-century after 1048 transformed both the papacy and western Christendom. Deliberately and innovatively international in outlook and personnel, central in the policies of the reforming papal Curia came the understanding that the church of Rome was synonymous with the universal church; that the pope held temporal as well as spiritual jurisdiction on earth as the heir to St Peter, to whom, according to the so-called Petrine texts in Matthew’s Gospel, Christ entrusted the keys of heaven and the power to bind and loose on earth and in heaven (Matthew 16:19). The more general reformist agenda included the improving of the morals and education of the clergy and the eradication of simony (paying for church office) and clerical marriage (a move both moral and economic, to protect church land from being inherited by non-clerical clergy children). An attempt was made to make secular priests more like monks, wholly distinctive from their lay neighbours and relatives, and loyally obedient to Rome.
This programme met fierce local opposition as it threatened the vested interests of lay and clerical patrons of private churches and monasteries; the habits of the mass of the secular priesthood; and the power of secular rulers to control the richest landed corporations in their regions. The most acute and bitter dispute developed with the king of Germany, Henry IV, whose accession as a minor had forced the reforming popes to seek independence from the German throne in order to protect themselves from Italian enemies. At issue were imperial rights in choosing a new pope; papal rights in approving the choice of emperor; and, more directly, the authority over appointments and control of the church in imperial lands in Germany and north Italy. The dispute was encapsulated in the ceremony of investing, i.e. giving newly consecrated bishops the ring and staff, symbols of their spiritual dignity. Traditionally in Germany, and elsewhere, kings performed this ceremony. Uniquely for a layman – and inconveniently for church reformers – kings were also consecrated, ‘the Lord’s Anointed’. The right to invest with the ring and staff became iconic, hence the name given to the dispute and the wars it generated, the Investiture Contest, although in reality the disagreements were both more mundane – control of church wealth and patronage – and sublime – the spiritual health of those who administered the Sacraments and ‘the right order in Christendom’.
This was much more than a theological spat. The power of the German kings relied heavily on control of the church, especially in Saxony. A revolt there in 1076 gave the most belligerent of the reforming popes, Gregory VII, an opportunity to put pressure on Henry IV to make concessions by publicly challenging his right to rule, claiming the pope possessed a plenitude of power that included the right to depose unsuitable monarchs, including emperors. The intransigent Henry IV was excommunicated in 1076 and again in 1080. Rival kings were put up by the papalist and anti-imperialist party in Germany. The ensuing war spilt over into Italy. In 1084 Henry IV invaded, captured Rome, installed his own anti-pope and forced Gregory VII to find refuge with the Norman conquerors of southern Italy. Over the subsequent decade, Henry’s anti-pope held sway in Rome, supported by repeated imperial forays south of the Alps. The background to the First Crusade lay in this conflict, as Urban II sought to use the mobilization of the expedition as a cover to reclaim the pope’s position in Italy and demonstrate his practical leadership of Christendom, independent of secular monarchs. The slogan of the papal reformers was ‘libertas ecclesiae’, ‘church freedom/liberty/rights’. This provided the central appeal of Urban II’s summons of 1095, when he called on the faithful to go to ‘liberate’ the churches of the east and Jerusalem. The crusade is impossible to understand outside of this context of more general church and papal reform. It was ironic that, at the very time they were asserting universalist claims, the reforming popes could never be entirely secure in Rome itself. Local nobles, deprived of control of the lucrative office of the papacy, German and pro-imperialist invaders and other Italian political rivals forced successive popes into temporary or near-permanent exile over the century following Gregory VII’s exile. It was only after he had launched the First Crusade in 1095–6 that Urban II was himself able to establish his residence in the Eternal City.