The documentation related to inquisitorial practice included trial transcripts, consultations, sentences, manuals and accounts. But while this documentation was a key ingredient in inquisition’s power, the relationship between these sources and our knowledge of medieval heresy is complex.

This chapter surveys violence imposed by medieval western-European Christians upon their chief religious “others”: heretics, Jews, and Muslims. Modern scholars have often found it useful to understand such violence collectively, echoing medieval Christians’ own frequent grouping together of those “others.” Yet it is important to disassemble the differences in why and how Christians wielded violence against each, and to recognize how violence took variegated forms, was committed by diverse actors, and resulted from multiple, coexisting motivations. Violence against Jews interpenetrated with their increasing demonization in Christian polemic and with their subject status in Europe. Both church and state, increasingly ambitious institutions, assisted in the general transformation of European Jews from protected minorities to not “real” Jews rightly deserving toleration. Violence against heretics (a more subjective identity than that of Jews and Muslims) was only rarely and early the object of mob violence. That was soon succeeded by “crusade” and the institutional violence of inquisitions, which owed a debt to monastic and penitential violence. While Christian violence against Muslims in Europe was geographically limited, key there was the evolution of Muslims from rulers to ruled, and even an acceptance of Muslims as agents of violence. Despite the varying circumstances, motivations, agents, and forms of Christian violence against all three, it was nevertheless embedded within a universalizing Latin-Christian theology and ecclesiology.

Even as state persecution has shifted its focus to who people are, rather than what they believe, the modern world can still look a little medieval. In 2013, centuries after the Jewish community in Amsterdam in 1656 imposed its most severe ban upon the philosopher Baruch Spinoza (1632–77) for heresy, the community considered revoking it. The final decision was to let the ban remain in force. As Chief Rabbi of Amsterdam Pinchas Toledano asked, “Does freedom of speech mean that we in our synagogue should spread the denial of God's existence to the extent that it destroys our heritage and the pillars on which Judaism rests? ” Ibn Taymiyah may have died under a cloud of heresy in 1328, but modern Islamists have discovered in him an inspirational defender of Islam's purity, opposed to coexistence with, and the influence of, non-Muslims. Modern Christian denominations, both Catholic and Protestant, still occasionally conduct heresy trials over matters of theology, social teaching, and ecclesiastical discipline.

“The pillars on which Judaism [and Christianity, and Islam] rest” – whether sacred text, tradition, reason, direct revelation, collective consensus – are still, often frustratingly for believers, both fragile and contested, and indispensable. The individual can still be set against the community, and toleration can discover its limits in the essential, yet oddly changeable, foundations of faith. Our medieval events left legacies for modern Judaism, Christianity, and Islam, even as believers grapple with some of the same questions about right and wrong belief that their predecessors did. To understand better religious heresy in both the medieval and modern worlds, we should step back and take stock. What are the conclusions from our history of medieval heresies?

We should note first some differences and similarities among these histories in all three religions. The most obvious, and important, difference is a stateless Judaism, with Jews living in minority communities under Christian and Muslim rule.

The Prophet Muhammad once predicted that as “the Jews are divided into seventy-one sects [and] the Christians into seventy- two, my community will be divided into seventy-three sects.”

Give or take a few sects, Muhammad's prophecy was correct. The three major religions of the Middle Ages had many things in common: All balanced sacred texts with commentary and interpretation that sought to translate lessons composed in a particular time with the always-moving pace of history. All had competing systems of religious leadership and authority confronted with vibrant, dynamic, lived religion. Christians, Muslims, and Jews were all somewhere, at some point, a religious minority. And all experienced the conflicting pulls of unity and diversity of which heresy was both by-product and accelerant. Diversity and difference, as Muhammad alluded, was only to be expected. The problem was that of unacceptable difference.

This book is a comparative history of heresy, and of responses to it, in the three major religions of the Middle Ages. In scholarship, “medieval heresy” usually connotes the Latin Christian heresy of Europe. Judaism, Islam, and even Greek Christianity – estranged from its Latin sibling by language, culture, and custom long before their schism in 1054 – have tended to fall out of the story, in part because of the inherent challenges involved in comparative history. Language, mentality, and circumstances differ, and even the most obvious similarities need to be understood in context, or can mislead. We'll describe below how this book will try to overcome those challenges. But the value of attempting our comparative history outweighs its risks. Judaism, Christianity, and Islam have never been hermetically sealed religions, and recent scholarship has emphasized their contact, exchange, and coexistence on the ground in the Middle Ages. Acknowledging the frequency and depth of that interreligious contact has two chief consequences for the history of medieval heresy.

In the early 440s, Salvian of Marseilles (c. 400–c. 480), known as a “teacher of bishops,” surveyed with great distress the changing world of the Roman Empire in the West. His On the Government of God was a sad record of failures, past and present: the Israelites of the Old Testament; his contemporary Latin Christians. To Salvian's eye, the religious landscape of the late Roman Empire was dark. Roman orthodox Christians were sinners, spurning God. And when Salvian wrote, the Germanic peoples then well advanced in transforming the empire, through settlement and conquest, were either pagans or heretical Arian Christians. Uneducated and unromanized barbarians, sighed Salvian, “follow blindly” whatever someone tells them is the truth, and in this way they had fallen into the heresy of Arianism:

What made this worse was that their heresies “spring originally from the false teaching they received from the Romans, and the inception of heresy among them becomes another heavy charge against us.” If orthodox Romans were sinners, and Germanic Christians accidental heretics, then Roman heretics were the worst of all: “their lack of faith makes them worse than the Romans, and their disgraceful lives than the barbarians.” Given all these failures, it was “easy” for Salvian “to estimate what the whole Roman state deserves”: a just punishment from God, like that Salvian was witnessing in that state's slow collapse.

Sometime before 1391, an anonymous writer against the Waldenses threw at them a familiar charge: because they were divided, their religious beliefs must not be true. God was unity and harmony, not fragmentation and weakness. As we've seen, this criticism was often used throughout the Middle Ages by Christians, Jews, and Muslims alike – with the critics usually ignoring their own religion's splits and diversity. However, this anti-Waldensian polemicist gave the traditional accusation a decidedly national spin:

This accusation referred to the schism that had broken the Waldenses in 1205, which had split the group into French and northern Italian branches. But it also reflects a very late-medieval way to think about and to organize people, one in which heresy was deeply engaged. We see in the late Middle Ages an increasing consciousness about people as naturally distributed into nations, with vernacular languages as an important component of that identity.

Certainly, persons everywhere had long understood and described themselves (and others) as different kinds of collectives, whether “people” or “nation.” We might recall from Chapter 3, for instance, twelfth-century Muslim heresiographer al-Shahrastani, who observed that humans could be grouped by language, ethnicity, or geography in addition to religious creed. But something began to change in the late Middle Ages.

In 833, ‘Abbasid Caliph al-Ma’ mun (r. 813–33) instructed the governor of Iraq to launch an investigation into wrong belief. The governor, Ishaq ibn Ibrahim, was to summon several judges and find “out from them their beliefs about God's creating and originating the Qur'an in time.” They should be warned that those not agreeing with the caliph's own belief – that the Qur'an was created – would lose public status and position. Judges whose orthodoxy was assured should then, in turn, be ordered to “interrogate closely the legal witnesses in their sphere of jurisdiction and to question them about their knowledge of the Qur'an; then [they are] no longer to recognize the validity of the testimony of those failing to affirm or hold the view that the Qur'an was created and originated in time.” Once Ishaq ibn Ibrahim received reports from the judges, he should himself write to the caliph to communicate “the results of their enquiries.” Finally, the governor was instructed to “keep a close oversight [upon] them and search out what they have been doing.” In these examinations, those who had formerly held that the Qur'an was uncreated should repent publicly; those who refused would be executed.

Caliph al-Ma'mun's “inquisition” (mihna) lasted several years, and in many ways resembled the more famous Christian heresy inquisitions that would begin in earnest in the thirteenth century. Suspects were interrogated; publicly acknowledged their error; punished (and possibly executed) if they didn't; and watched afterwards. Although there were differences – notably the lack of foundation in Roman law – it is not too much to say that these trials were the first heresy inquisitions of the medieval world.

In the usual narrative of medieval heresy, the early Middle Ages are rather empty, neither very useful nor enticing. Especially after the combative liveliness of the centuries we have just encountered, this period can seem too quietly devoid of controversy.