Answers that rely on the alleged barbarism of the times or the brutality or narrowed-mindedness of individual churchmen or rulers are unsatisfying. We need to understand why religious dissent was so alarming that political and religious authorities resorted to violent repression.

In Persecution and Toleration, we outline why states often had an incentive to enforce religious conformity.

Suppose the ruler wants to pass a law. The religious authority can choose to legitimate this law or to oppose it. If the religious authority opposes it, the law will be seen as illegitimate, and the ruler will face unrest or opposition in attempting to enforce it. If the religious authority legitimates the law, then compliance with the law will be greater and the law will be enforced at a much lower cost for the ruler. Rulers therefore have a good reason to want legitimacy. Because religious authorities were the most powerful source of legitimacy in the premodern period, it was natural for rulers to rely on religious legitimacy.

Rulers can bargain with religious authorities to obtain legitimacy. One way to do this is to enforce religious conformity. This provides a natural framework for studying religious persecutions.

One insight is that persecutions are necessarily political. The justification for persecution can vary. Secular authorities will persecution in terms of secular arguments. Religious authorities may persecute on religious or doctrinal grounds. But structurally these persecutions will resemble one another.

A second key argument is that some form of religious repression was the default in the premodern world but outright persecution was, in fact, quite rare. The default level of religious repression we characterize as a state of conditional toleration. Religious differences were usually tolerated, but only conditionally. Outright persecution was quite rare. But the threat of persecution played an important role in enforcing religious conformity, restricting dissent and providing states with legitimacy.

How general is our account? Is this story only applicable to Western Europe? Or to monotheistic societies? Can it explain the persecution of Christians in pagan Rome or the persecution of Christians in 17th century Japan? And what distinguishes religious persecutions from other persecutions?

To address these concerns, consider the persecution of Christians in the Roman Empire. Historians such as Candida Moss downplay these persecutions (here). Catherine Nixey’s The Darkening Age — reviewed positively in the New York Times —for example, writes:

“The idea, therefore, of a line of satanically inspired emperors, panting for the blood of the faithful is another Christian myth. As the modern historian Keith Hopkins wrote, ‘the traditional question: “Why were the Christians persecuted?” with all its implications of unjust repression and eventual triumph, should be re-phrased: “Why were the Christians persecuted so little and so late?”

Nixey correctly cautions the reader not to view Christian accounts of the death of martyrs as historical accounts. But her argument is a larger one. To her mind, the persecution of Christians was not a religious persecution. Commenting on the Roman governor Pliny’s decision to persecute some Christians, she writes:

“Pliny’s problem with all of this is not religious. He is not upset because Jupiter has been neglected, or Hera has been slighted: he is upset because the citizens of his province are becoming disgruntled by the Christians’ behaviour . . .”

“. . . Even the locals who were forcing Pliny’s hand might not have been complaining about Christians for religious reasons either: it has been speculated that what was really upsetting them was not theology but butchery. Local tradesmen were angry because this surge of Christian sentiment had led to a drop in the sales of sacrificial meat and their profits were suffering: anti-Christian sentiment caused less by Satan than by a slow trade in sausage-meat.”

Because Christians were punished as pests and social deviants, rather than for reasons conventionally identified as religious, Dixey suggests this was a simple matter of“law and order”. If anything her sympathies appear to be with the Roman governor responsible for prosecuting Christians:

“What should Pliny do with these odd people? Trajan’s reply is brief and to the point. He doesn’t get into theological or legal debates about the legal status of Christianity (to the disappointment of later scholars); nor does he (thus confounding the martyrdom tropes) fulminate against the Christians. He does agree with Pliny that those who are proved to be Christian ‘must be punished’ — though for precisely what charge is unclear. He also adds that ‘in the case of anyone who denies that he is a Christian, and makes it clear that he is not by offering prayers to our gods, he is to be pardoned as a result of his repentance however suspect his past conduct may be’. Roman emperors wanted obedience, not martyrs. They had absolutely no wish to open windows into men’s souls or to control what went on there. That would be a Christian innovation.”

This hardly not exculpates the Romans or implies the persecution of Christians was a myth. Nixey is correct that the Roman authorities were unconcerned with what Christians believed. But she is wrong to suppose that this is the defining characteristic of religious persecution. And the urge to downplay the persecution of Christians suggests other anachronistic instincts are at work. After all, no-one denies that Christians were killed, often horrifically, in the Roman persecutions (for a critical review of Moss’s book, on which Nixey relies, see here).

Theologians were, of course, concerned with wrong beliefs. But the reason why religious dissent became a major concern to both secular and religious authorities in medieval Europe was precisely due to the threat heresy posed to the established social and political order.

Consider another example from medieval Europe. Norman Cohn’s Pursuit of the Millennium explains the threat heretical movements posed to political order. Focusing on the most revolutionary millennium sects — movements that envisioned the last days as at hand, and took action to herald their coming — Cohn’s text vividly captures both the appeal as well as the radicalism and violence of these movements. Describing the manifesto of the “Revolutionary of the Upper Rhine”, Cohn writes:

“the route to the Millennium leads through massacre and terror. God’s aim is a world free from sin. If sin continues to flourish, divine punishment will surely be visited upon the world; whereas if sin is once abolished, then the world will be ready for the Kingdom of the Saints. The most urgent task of the Brethren of the Yellow Cross is therefore to eliminate sin, which in effect means to eliminate sinners . . . To achieve that end assassination is wholly legitimate: ‘Whoever strikes a wicked man for his evildoing, for instance for blasphemy — if he beats him to death he shall be called a servant of God; for everyone is in duty bound to punish wickedness.’ In particular the Revolutionary calls for the assassination of the reigning Emperor, Maximilian, for whom he had an overwhelming hatred.”

Such beliefs were a threat to all established authority. Church authorities were naturally concerned with monitoring belief and practice. But heresy also posed a potent threat to secular authority.

Of course, many people in medieval society had incorrect and unorthodox religious beliefs. What principally concerned the Church was not ignorance but heresy: obstinately holding beliefs that directly contradicted Church teachings.

Heresy was feared because it was a source of disorder. Religious dissent had the potential to unleash revolutionary violence and social chaos. This was one reason why Martin Luther recanted his earlier support for religious liberty during the Peasant Revolt.

Arguments for enforcing religious conformity went deeper than the fear of revolutionary violence. Such was the importance of the Church to the social and political order that all challenges to Church authority were perceived as threats to society.

Consider the doctrine of apostolic poverty — which emerged in the 11th and 12th centuries as the Commercial Revolution was transforming the European economy increasing urbanization, trade, wealth, inequality and also poverty. Shocked by the growing gap between the rich and the poor, adherents to this doctrine aspired to the simple poverty of Christ’s followers. They lived without property or money and they were critical of the wealth accumulated by the Church.

The fact that the Church was wealthy did not, of course, imply that Churchmen were not devout or dedicated. The problem was, however, that the Church was also a political institution. Many bishoprics were the preserve of the nobility who would jostle to ensure that their younger sons became influential churchmen. These prelates were expected to be the equal of the secular nobles, to entertain lavishly, and to dress splendidly. Taken too far, therefore, apostolic poverty threatened the legitimacy of the Church and its relationship with secular authority.

Through mendicant orders such as the Franciscans, the Church could accommodate these demands and concerns. But groups who directly attacked the legitimacy of the Papacy itself, such as the Waldensians and the Spiritual Franciscans could not be tolerated. The leader of the Spiritual Franciscans, Angelo da Clareno denied that Pope John XXII was pope, a direct challenge to the legitimacy of the Church. Precisely because of the threat they posed to the church and state alliance — and not because of their theological beliefs, which were unremarkable — the Spiritual Franciscans had to be repressed.

Were the concerns of the Roman Emperors so different from those of medieval rulers and churchmen? Religion was not a private affair in antiquity. It had political consequences; it mattered for the fate of the Empire. The first Empire-wide persecution of Christians occurred under Decius (r. 249–251). Decius’s response to the political crisis facing the Empire — invasions from both Persia and the Goths — was a revival of the state religion and the imperial cult.

Claiming that Roman persecutions of Christianity were not religious but political, as Moss and Nixey do, is misleading; all persecutions are political. Because it began as a persecuted cult, Christianity as a religion contained many potent arguments against religious persecution. For these reasons, it was probably less predisposed to persecution than many other religions. Nevertheless, the fact that the medieval Church eventually came to persecute dissent points to deep, structural, political economy factors that made religious freedom impossible. It this these factors that are the subject matter of Persecution & Toleration.