During the 12th century, communes, or city-states, developed throughout central and northern Italy. After early beginnings in cities such as Pisa and Genoa, virtually every episcopal city in the north formed a communal government prior to 1140. The origins and developments of communes are complex, and attempts to explain them in simple terms are doomed to failure. The emphasis of 19th-century liberal historians on communal revolts against ecclesiastical repression as well as the later Marxist focus on class conflict in the development of the communes have proved too narrow. They have failed to recognize both the many different causes of violence in the communes and the diversities within the communal movement. Violence resulted from such diverse factors as the conflicting interests of ecclesiastical institutions, the complex ties of loyalty that bound men to one another and to the institutions of their society, and shifts in the distribution of power.

The Investiture Controversy focused the efforts of the higher clergy on consolidating their rights against infringement not merely by the lay aristocracy but also by ecclesiastical competitors. Examples of conflict from various places and periods show how relationships changed dramatically, often within a short period. At Brescia, for example, the bishops, who contested the abbots of Leno for control of the church of Gambara, drew support from a faction of the milites, the landed aristocracy, as well as from the popolo, which was composed of professional people, craftsmen, and merchants. Elsewhere, local circumstances dictated other alliances. During the period in which the cities were expanding their power into the contado (the region surrounding the city), elements drawn from town and countryside continually struggled for control of the commune. Alliances shifted depending on the success or failure of these efforts. At Lucca the bishop and the commune were jointly concerned about the claims of the Abbey of Fucecchio because of its ties to neighbouring Pisa. But the efforts of bishops to establish their rights in the contado could also provoke conflict with the commune. Much depended on the makeup of the commune, which varied widely not only from city to city but also from period to period. The relative influence of urban merchants or rural landholders depended on the size of each group within a particular community. Where one group was small, it allied itself with others. The quest for power led to shifting and, at times, strange alliances; for example, at Brescia in the early 13th century, one faction of local magnates drew support from heretics. Even when the commune brought together various factions in sworn associations, it still faced not only the problem of its enemies in the city and countryside but also that of the fragile nature of the coalition on which it rested. Communes created elaborate systems of checks on power that aimed to prevent dominance by any single faction. Term limits were imposed to force changes in the ruling councils. The consuls, so named from Roman precedent, similarly faced limits on their power.

From its inception it was clear that communal government aspired not merely to political independence but also to control of the contado. As a result, a complex relationship developed in which the contado found markets for its products, offered opportunities for investment for city dwellers, and suffered oppression from urban interests. The city, in turn, offered opportunities to the people of the countryside and helped to ensure a measure of security. There is probably no way for scholars to establish the balance of benefits and disadvantages, but one may be certain that it shifted continuously, depending on region, local conditions, and the general economic climate at a given time.

It is evident, however, that the communes of northern and central Italy benefited from the Investiture Controversy. The ineffectiveness of imperial power in Italy during the first half of the 12th century, which favoured the development of the communes, stemmed largely from the struggle over investitures and the attendant political instability in Germany. These external factors, however, do not in themselves account for the rise of the communes. For that, one must turn to internal factors, particularly the dynamics among various factions and the social dislocations during and following the Investiture Controversy that accompanied rising populations and increased prosperity. The reformers’ success in weakening the bonds between church and empire remained a decisive force throughout the 12th century and well into the 13th century. The partisan perspectives of contemporaries oversimplified the Investiture Controversy, showing it either as a struggle for the freedom of the church from lay power or as an effort to preserve the traditional—that is, imperial—order within society. Actually, however, given the complex network of local loyalties within both church and secular society, the controversy fragmented loyalties of both the clergy and the laity. If the old order was weakened, it was not merely a secular order that lost but an ecclesiastical order as well. Nor was it merely the unreformed monasteries and imperial bishoprics that lost; at times, communal authority emerged stronger than any ecclesiastical power in the region. Certainly, by the early 13th century this was true in Genoa, and it was soon to be the case in Milan, Florence, Bologna, and elsewhere.