Having arrived in southern Italy in small groups just prior to 1020, perhaps in part as petitioners at the court of Pope Benedict VIII and in part as pilgrims returning from the Holy Land, Normans joined Lombard rebels in their effort to throw off Byzantine rule in Bari. Although this proved a failure, Norman mercenaries continued to enlist in the armies of various southern Italian rulers. In 1030 Sergius, duke of Naples, granted the county of Aversa to the Norman Rainulf in return for his support against Pandulf of Capua. Rainulf was able to add Gaeta to his holdings, and his nephew, Count Richard, who had succeeded to Aversa in 1047, added the principality of Capua. The next wave of Normans, led by the sons of a lesser Norman landholder, Tancred of Hauteville, undertook a full-scale effort to conquer the south. Robert Guiscard, Tancred’s fourth son, assumed a commanding role in southern Italian affairs.

Leo, who remained committed to the imperial ideal, opposed the Normans because he felt that they threatened not only Rome and the papacy but also the interests of the German emperor and relations between East and West. The continued expansion of the Normans in southern Italy and their aggressive assertion of titles—William de Hauteville (William Iron Arm), for example, assumed the title of count of Puglia—influenced Leo to forge an alliance of papal, imperial, and Byzantine forces. With himself in the company of imperial troops but without awaiting the arrival of promised help from the Byzantines, he met the Normans at Civitate on June 16, 1053. The ensuing defeat was a deep humiliation for Leo, though the Normans treated him with respect. The forced peace profoundly disturbed the balance that he had sought in Italy.

His policy also received a serious setback from the conflict that arose in Constantinople between his legates (Humbert of Silva Candida, Frederick of Lorraine, and Peter, archbishop of Amalfi) and the Eastern patriarch, Michael Cerularius. Scholars differ on the reasons for this conflict, but it arose at least in part from the clash between the papal policies of Latinization of the churches in southern Italy and the claims of Constantinople to jurisdiction in that region. Scholars have often viewed the mutual excommunications launched by the legates and the patriarch in 1054, after the death of Leo, as the beginning of the schism between the Eastern and Western churches; however, that view probably overstates the significance of these events. More particularly, the breach with Constantinople closed the door on the approach taken by Leo IX and led to a major shift in papal policy in favour of the Normans.

Leo’s successor, Pope Victor II (1055–57), formerly the bishop of Eichstätt (Bavaria), the fourth pope chosen under the aegis of Henry III, tried to follow in the footsteps of his predecessor. But the death of Henry in 1056 and the failure of Leo’s policies in southern Italy limited his role. The Normans continued to strengthen their position in southern Italy. Victor II thus was constrained not only by the failed mission to Byzantium but also by the threat from the south. Moreover, on Henry III’s death, the empire came to his six-year-old son, Henry IV (1056–1106), with his mother, Agnes of Poitou, as the regent. Although the succession to the throne was not in doubt, the inevitable intrigues surrounding the regency deprived the papacy of imperial support. When Victor died in 1057, a party of the reformers moved to take advantage of this vacuum. They acted quickly to elect Frederick of Lorraine as pope, under the name Stephen IX (or X; 1057–58), without any effort to consult the regency.

Stephen, who had succeeded to the papacy while abbot of Montecassino, summoned Peter Damian from the monastery of Fonte Avellana to become cardinal-bishop of Ostia. The election of a pope whose brother had been a rebel against the regency suggests that the strong ties that had bound the reform movement to the empire had been somewhat weakened. At the same time, the position of the reformers in Rome was also weakened. When Stephen died in 1058, the Roman nobles supported the election of Bishop John of Velletri as Benedict X (antipope 1058–59), thereby attempting a return to the pro-aristocratic and pro-Roman policies of Benedict VIII and Benedict IX. These circumstances forced the reformers to seek support from the empress Agnes. Their candidate, the Burgundian bishop of Florence, Gerard, was installed on the papal throne as Pope Nicholas II (1059–61).

The reign of Nicholas was pivotal. Not only did Nicholas preside over a major shift in the papacy’s relations with the Normans but he also issued a decree in 1059 regulating future papal elections that began the process of concentrating electoral powers in the hands of the cardinals. The consequences of the papal defeat at Civitate in 1053 had already laid the foundation for a change in papal relations with the Normans. Leo IX had earlier appointed Humbert of Silva Candida as archbishop in Sicily and now entrusted the conquest of Calabria and Arab-dominated Sicily to the Normans with the provision that they should remain a hereditary fief of the papacy. This assertion of papal overlordship, often read solely in political terms, represented an effort on the part of the papacy to ensure its claims to jurisdiction over the churches of the still-unconquered lands against the claims by Constantinople. Nicholas’s Norman alliance was less a dramatic diplomatic revolution than a response to the changes that confronted the papacy from Civitate onward. The alliance safeguarded papal interests in the south, ensured a measure of stability in Rome during a period of imperial impotence, and promised the independence that the reformers had sought in their notion of libertas ecclesiae (i.e., church immunity from secular control and jurisdiction). But the weakness of the empire also led the papacy to seek support in northern Italy.