Paolo Brezzi was born December 18, 1910, in Turin, Italy, and obtained the degree of Doctor of Letters at Turin State University. He has taught. philosophy and history in state graduate schools and medieval history at various Italian universities. At present, he is ordinary professor of Church history at the University of Naples, Italy. The author of a number of publications in political history, political doctrines and Church history, he is history consultant of the Sacred Congregation of Rites, vice-director of the well known historical review Studi Romani, and member of various commissions on Italian history. This book is not intended to be a history of the popes, narrating even briefly the life and activities of each individual titular; neither is it an enumeration of the religious, political, civil and cultural undertakings initiated by the popes or developed under their leadership. The immense quantity of such material could not possibly have been brought within the scope of this volume. Nor are there wanting works of this type, more or less voluminous and reliable. The aim of this study, instead, is to trace the evolution of the papacy-specifically, the historical development of the papal institution as seen against the setting of its various periods and exemplified by its more typical representatives-in order to ascertain whether its perennial existence is the result of favorable historical circumstances, of cleverness and intrigue, or of an element of consistency and inevitable continuance inherent to the institution itself. In this book, references to persons and events presuppose that the reader is generally familiar with them and that he will consult larger works if he desires more extensive details. In view of the nature of this study, we cannot be expected to demonstrate the validity of the principles upon which the papacy rests; that is, the possibility and the fact of a revelation, the intention of Christ to establish a Church, the characteristics of such a society, and like points. But, assuming these as demonstrated, we shall see that ever since the beginning of the papacy a principle was laid down which, under the force of circumstances and not without contrasts, evolved in the course of the centuries with a logical application and an ever increasing influence. This principle consists of a special power that is maintained in the Church by virtue of a lawful succession to the head of the apostolic college, and is made the standard of all the activities of the faithful and of the priestly hierarchy. It stems from the concept of "vicariousness," which, whether the proper corresponding term is expressed or not, constitutes the foundation of papal activities and furnishes the light in which these are explained and understood. Disregarding the better-known but less essential aspects of this institution (a complexity of tasks performed in the most diversified fields of human endeavor), the central fact remains that pontiffs exist, rule and promote activities as representatives of Christ, whom they perpetuate visibly down through history. It is quite true that for a long time there were no such close ties of dependence between clergy and pontiff as exist today; nor did local Christian communities always feel strongly in their loyalty to Rome or accept its controls. But such facts do not in any way invalidate our position, because what really matters is to establish whether the transition of the papacy from its ancient to its modern status is a natural evolution of a vital germ, or an innovation and an arbitrary usurpation.