Already in the second half of the 11th century, studies of Roman law underwent a revival at the University of Bologna under the influence of the jurist Irnerius and his school. Earlier emperors had, in fact, employed Roman law in their judgments and legislation. But Frederick was more conscious of its importance as a source justifying imperial actions. He issued a special privilege for scholars studying law, the so-called “Authentica Habita” (c. 1155), and played a leading role in the gradual evolution of the law schools at Bologna. Roman law, however, was merely one source that contributed to the development of more clearly defined social and political institutions in the 12th century. The profound changes occurring in Italy in this period made innovation inevitable. Communes everywhere were experimenting with new political forms, often concealing their novelty behind traditional names. In the Norman kingdom the effort to fashion royal institutions for disparate regions and populations led not only to a layering of administrative institutions within the royal court but to a great diversity from one region to another. Everywhere, attempts at reconciling widely divergent legal and customary arrangements demonstrated a desire for legal uniformity; the view that each group should live by its own law no longer served the needs of society. More and more, Roman and canon law provided sources useful for reconciling differences. Frederick Barbarossa saw himself as an agent of unification. Although he represented the traditional order and was so viewed by his numerous enemies in Italy, he identified himself with the changing order that was emerging in the mid-12th century. Roncaglia was a new constitutional statement despite its conservative reliance on regalian right.

Northern Italy

Roncaglia laid the foundation for a new regime in northern Italy. The regalia produced an enormous income from such sources as minting coinage and collecting tolls, making Frederick the wealthiest of all European monarchs. This led him to reconceive the position of Italy within the empire. His aggressive policies could not help but alarm Milan and its allies, and they also caused profound concerns for the papacy. The death of Adrian IV in 1159 revealed a division among the cardinals. A pro-imperial group supported Octavian of Monticello, while the opposition chose Cardinal Roland of Siena. Amid angry recriminations, the two claimants assumed the papal title, Octavian as Victor IV (antipope 1159–64) and Roland as Alexander III (1159–81). At a poorly attended council in Pavia, Frederick abandoned his neutrality and supported Victor IV. But Victor found little support beyond the boundaries of the empire. Even Bishop Eberhard of Bamberg, one of Frederick’s closest advisers, made his acceptance of Victor conditional on Victor gaining recognition from the whole church. Nevertheless, Frederick’s support was sufficient to give life to the schism. Alexander III relied chiefly on France, England, the Lombard cities allied with Milan, and the Normans in southern Italy and Sicily. On the whole, Frederick’s position was the weaker one, but he refused to make concessions. Failing to win over Louis VII of France, he journeyed once again to Italy, only to face strong opposition from the patriarch of Grado, who organized the anti-imperial League of Verona. When Victor IV died in 1164, Rainald of Dassel arranged for the election of the strongly imperial Paschal III (antipope 1164–68) as a rival to Alexander III. But Alexander also faced difficulties. The controversy between King Henry II of England and Archbishop Thomas Becket threatened to deprive Alexander of English support. Moreover, feeling increased uncertainty about his position in France, where he had fled to in 1162, Alexander returned to Rome in 1165 and sought support from the Normans. The death of William I of Sicily in 1166 prevented the realization of this goal, and he once again had to look to France as his mainstay.

Frederick sought a decisive solution in Italy in 1166. He marched with a large force to Rome, but a devastating outbreak of malaria among his troops while in the city put an end to the emperor’s plans. In 1167 the Lombard cities formed a league to defend against Frederick’s expedition that included Milan, Venice, Padua, Mantua, Brescia, and Lodi.

Despite his setback, Frederick was determined to stay the course. Indeed, by this time, he could hardly turn back without accepting a near-total surrender. Failing to muster support in Germany, Frederick was forced to rely on the limited resources left to him. On May 29, 1176, he met his enemies at Legnano in northern Italy. The army of the Lombard League, under the leadership of Milan, and Frederick’s army engaged in a pitched battle, in which the supporters of the empire were thoroughly routed. Accepting the realities created by his defeat, Frederick waged a diplomatic campaign that secured the remarkable treaty concluded with Alexander (whom he now recognized as pope) and the Lombard communes in Venice in July 1177. This agreement settled little definitively, but Frederick obtained a six-year truce with the Lombards and was able to hold onto the Mathildine lands in Tuscany for 15 years. He restored his position in Germany and recovered from the losses endured in Rome. In 1183 Frederick converted the truce of Venice into the Peace of Constance, in which he renounced the regalia claimed at Roncaglia but preserved the administrative rights of the crown. From defeat he thus managed to salvage a considerable portion of his imperial power.

Frederick launched his final expedition to Italy in 1184, where he met with Pope Lucius III (1181–85). He also witnessed a diplomatic turnabout on the part of the Norman ruler, William II (1166–89), who espoused his aunt Constance, the daughter of Roger II of Sicily, to Henry, the second son of Frederick. Although Constance was not expected to inherit the Sicilian throne, because William and his queen might still have children, the implications of the agreement were nonetheless momentous. The papacy found itself faced with an intolerable situation. Frederick, now aiming to build a power base in Tuscany instead of Lombardy, attempted to annex the Mathildine lands. Although he failed in this, he secured the spolia (spoils) and regalia of vacant bishoprics and abbacies from Clement III (1187–91). Yet Frederick did not live to consolidate this effort. The defeat of the Crusader army at Ḥaṭṭīn in the Holy Land in July 1187 and the subsequent fall of Jerusalem sent a great shock through the West and inspired the Third Crusade. Frederick took the cross; the kings of England and France followed suit. Frederick Barbarossa drowned in the Saleph River in Anatolia on June 10, 1190. The Crusade was able to save ʿAkko (Acre) and assure the continued Crusader presence in the East, but it left Jerusalem in Muslim hands.