01/26/2012 12:08 pm ET Updated Mar 27, 2012

How Popes Have Shaken The World (PHOTOS)

In an exclusive excerpt from his new book 'Ten Popes Who Shook the World,' one of the world’s most highly regarded historians of Christianity discusses the historic power of the papacy.

The papacy is an institution that matters, whether or not one is a religious believer. The succession of the popes, all 262 of them, is the world’s most ancient dynasty. The Roman Empire was young when the popes first emerged onto the stage of history, and the earliest references to them, in the late second century, already claim for the bishop of Rome a status greater than that of any other Christian leader. Eighteen centuries on, the popes exercise a quasi-monarchic rule over the world’s largest religious organisation. They touch the consciences, or at any rate the opinions, of almost a fifth of the human race. The papacy has endured and flourished under emperors, kings and robber barons, under republican senates and colonial occupations, in confrontation or collaboration with demagogues and democrats. And by hook or by crook, it has survived them all.

The popes themselves have never been in doubt about the coherence of papal history, or its source. From the beginning they have claimed divine warrant for their office as an institution established by Christ himself, destined to endure as long as the human race. In the key papal text from St. Matthew’s Gospel, the papacy (in the person of St. Peter) is described as the rock on which the Church is founded, "and the gates of hell shall not prevail against it." (Read on after the slideshow for more from "Ten Popes Who Shook the World.")

Popes Who Shook The World

For non-Catholics, of course, the significance of the papacy stems not from its religious claims but from its impact on human affairs. Thomas Hobbes famously remarked that the papacy was "not other than the ghost of the deceased Roman Empire, sitting crowned on the grave thereof." The comment was certainly not intended as a compliment, but it encapsulated an important historical reality nonetheless. Through no particular initiative of their own, the popes inherited the mantle of Empire in the West; the papacy became the conduit of Roman imperial values and symbolism into the European Middle Ages. In a time of profound historical instability at the end of antiquity and in the early Middle Ages, the see of Peter was a link to all that seemed most desirable in the ancient world, custodian of both its sacred and its secular values. The papacy embodied immemorial continuity and offered divine sanction for law and legitimacy. So popes crowned kings and emperors and, on occasion, attempted to depose them. Even in the eighth and ninth centuries papal authority stood high, although the papacy was the prisoner of local Roman politics and many of the popes themselves were the often unlearned younger sons of feuding local dynasties.

The papacy stood outside the local entanglements of churches which were embedded in the social, political and economic structures of their societies. Submission and fealty to the papal "plenitude of power" offered great landed institutions like monasteries exemption from the more burdensome and immediate interference (and financial claims) of local bishops. The adjudication of the popes in the countless jurisdictional, doctrinal and disciplinary disputes of Christendom was a resource appealed to by all parties. Had papal authority not existed in the Middle Ages, it would have to have been invented.

Papal claims reached their height in the central Middle Ages, and were often turned by the popes into a platform from which to dominate the world. This tendency was already evident in the career of the great and forceful ninth-century pope, Nicholas I, who confronted and faced down emperors. It reached its most famous expression in the early 14th century with Boniface VIII, whose bull Unam sanctam declared that it was "altogether necessary to salvation for every human creature to be subject to the Roman Pontiff." Everything the modern papacy claims, and very much more besides, such as the papal deposing power, was claimed for the popes then.

In the high Middle Ages the popes most certainly shook the world. It was an 11th-century pope who first called on the armed force of Christendom to "liberate" the great pilgrimage sites of Jerusalem and the Holy Land from Muslim domination: the crusades were the result, inaugurating a centuries-long bloody episode whose consequences reverberate still.

In the centuries after this zenith of papal influence, the papacy went on insisting on the universality of its spiritual authority, but in reality it declined drastically, even among all the Catholic powers of Europe. The Renaissance popes could command the greatest artists and architects in Europe, and they created a Christian Rome whose glories were designed to outshine pagan antiquity, and to assert the claims of the papacy against dissent within and beyond the Catholic Church. But the spiritual claims of the papacy were complicated and, in the eyes of many, compromised by the fact that the popes all too often behaved like mere Italian princes, aggrandising their relatives (including their children) while exerting over the Church a hold which had as much dynasty as divinity about it. The rock on which the Renaissance popes founded their fortunes was not so much Christ’s promises to Peter, as the papal monopoly on the mining of alum, the rare mineral essential for the tanning of leather.

Large tracts of northern Europe repudiated papal authority during the Reformation of the 16th century. But the papacy, which even to Catholic reformers had seemed almost hopelessly corrupt, made a startling recovery. As Catholic institutions and Catholic doctrine came under threat, the popes emerged as a centre of continuity and a spearhead of renewal. Rome became both the executive centre and the symbolic focus of a resurgent and aggressive Catholic Counter-Reformation. But paradoxically, this very resurgence of papal energy triggered a reaction among the Catholic powers of Europe. They began to find irksome the ancient claims of the popes to intervene in secular matters. Popes of the time might have inhabited buildings that spelled out an almost megalomaniac vision of papal dominance, like the monstrous bronze baldachin that Pope Urban VIII raised over the papal altar in St. Peter’s, embossed with enormous heraldic bees from his own family’s coat of arms, but in reality the popes were in serious danger of being reduced to purely ceremonial significance. In 1606 Pope Paul V put the entire Venetian Republic under solemn interdict for what he saw as incursions on papal authority. Interdict was the popes’ most formidable weapon, a collective excommunication and ban that in theory halted the celebration of any sacraments and rites -– Baptism, the Eucharist, Marriage, Christian burial -– throughout Venetian territory. But the rulers of Venice called the Pope’s bluff, forcing the clergy to carry on as usual or be banished. After a year of deadlock, the Pope was forced into a humiliating climbdown. Underneath the elaborate deference of the Catholic world, the papacy and its often inconvenient religious demands were resisted. Cardinal Richelieu said of the Pope, "We must kiss his feet -– and bind his hands." So the kings and queens of Catholic Europe appointed their own bishops, taxed the clergy, policed contacts between the local churches and Rome, restricted the publication of papal documents, determined the syllabus in the seminaries and expelled or dissolved the religious orders as they pleased. And in all this the popes grumbled, protested and complied.

The modern papacy, therefore, with its unchallenged jurisdiction over the whole Catholic Church, is not the product of a steady evolution from simple beginnings, the natural growth of some essential acorn into a mighty oak. In a real sense it is, rather, the result of a historical catastrophe, the French Revolution. The Revolution swept away the Catholic kings who had appointed bishops and ruled churches, and once more made the popes seem the embodiment of ancient certainties. The hostile secular states that emerged in 19th-century Europe attempted to reduce the influence of the Church in public life, but they were happy to leave its internal arrangements to the Pope.

The most crucial and important practical power possessed by modern popes is arguably the right to appoint the bishops of the world, and thereby to shape the character of the local churches. It is salutary to remind ourselves that the popes did not possess this unchecked power in canon law until 1917, and the practice of direct papal appointment of bishops did not become general until the 19th century. Before then the Pope’s role in appointing bishops was not generally as universal pastor but as Primate of Italy or as secular ruler of the Papal States. The 1917 Code of Canon Law itself, which lies at the heart of papal domination of the modern Church, arguably owes at least as much to the Napoleonic Code as to Holy Scripture, and the exercise of papal authority in the modern Church is rooted in quite specific aspects of the institutional and intellectual history of the last 200 years.

Whatever its roots and its vicissitudes, papal influence over world events remains formidable. Popes no longer mobilise armies or launch crusades, but over the last century or so a greatly enlarged papal diplomatic corps of nuncios and apostolic delegates has secured for the modern popes powerful representation to most of the governments of the world, and in international bodies like the United Nations. Catholics form a fifth of the world’s population, and the Catholic Church is the world’s largest conglomerate of humanitarian and relief organisations. Those facts alone give immense significance to the opinions and actions of popes.

It was because they knew that the words of the Pope had the power to move millions that the Allies in the Second World War were so determined that Pope Pius XII should condemn Nazi atrocities. And with the rise of instantaneous modern communications and modern forms of travel, the popes have gained a direct and imaginative presence in both Church and world unthinkable in earlier ages. The capacity to translate that symbolic religious valency into world-shaking action was startlingly demonstrated by the crucial role of Pope John Paul II in the fall of communism in Poland and the wider Soviet bloc. For good or ill, the popes continue to shake the world.

Adapted from 'Ten Popes Who Shook The World' by Eamon Duffy, published by Yale University Press in November 2011. Reproduced by permission.

Eamon Duffy is professor of the history of Christianity, Cambridge University, and fellow and former president of Magdalene College. He is the author of many prizewinning books, among them 'Fires of Faith,' 'Marking the Hours' and 'Saints and Sinners.'