This chapter offers a critical narrative of the development of Arianism as a heresy from the fourth to the sixth century. It explores the changing meanings of the heresiological label, and the political and ecclesiastical contexts in which it was deployed, from the origins of controversy between Arius and Alexander in Alexandria through to the barbarian successor kingdoms of the post-imperial West.

This chapter introduces the main themes and scope of the volume, including discussing the origin of the concept of ‘heresy’, as well as outlining what aspects of it will and will not form the focus of the following chapters. It then provides a summary of the division of the volume into two parts and the particular topics and case studies contained in each.

This chapter suggests that the papacy dealt with Protestantism in various ways. It condemned the forty-one propositions of Martin Luther and then waited for the Council of Trent to condemn others. It used the institutions of preventive press censorship and of various inquisitions to check heresy. It sought the support of Christian rulers to prevent its spread, sending nuncios and legates to the rulers of the Holy Roman Empire, France, England, Scotland, Sweden, Denmark, and Poland–Lithuania to urge them to suppress heresy and to secure their loyalty by negotiating agreements on Church appointments and shared revenues and by offering military aid, efforts that had mixed success, or failed. Religious orders such as the Jesuits and Capuchins were also enlisted in the struggle. Leading Protestant reformers came to see the papacy as the Antichrist or foreign usurper.

This chapter examines two so-called transitional theologians who straddled the worlds of orthodox belief and learning and forward-looking scholarship and literary engagement. Johann Lorenz von Mosheim (1693–1755) and Johann Georg Walch (1693–1775) pointed the way to a new view of the Reformation, even if the results of their interventions went much farther then they intended. Mosheim’s History of Michael Servetus sought a type of transhistorical reconciliation between the eponymous Spanish heretic and John Calvin, who had him burned at the stake in Geneva. Mosheim tried to acknowledge the occasional brutality of Reformation-era Protestants while contextualizing the historical attitudes of an earlier era. Walch’s twenty-four-volume Luther edition was notable not only for rendering Luther’s language into a readable vernacular, but also for a long historical essay on Luther’s “accomplishments.” Walch sought to both acknowledge the genuine contributions of the first Reformer while also stripping away some of the mythical status that had accrued to Luther through generations of pious veneration.

The final chapter provides an examination of how the Merovingian world was shaped by opposition to paganism, heresy, Judaism, and, at the end, the new Islamic world of the Arab caliphate. The Franks (or at least some of them) had started as pagans themselves in the fifth century, and stories of conversion created important reminders of the journeys to salvation. Whether ‘real paganism’ is easily identifiable in stories or grave goods we may doubt. Similarly, the presence of heresy or Judaism can seem ambiguous when the sources are interrogated. But the creation of Frankish Christianity relied on its contrasts and those fed to it by the Byzantine Empire. Through Merovingian accounts of religious conflict we can discern how the Frankish kingdoms saw their place in the wider world.

The book is devoted to the relationships between Nicene and Homoian Christianities in the context of broader religious and social changes in post-Roman societies from the end of the fourth to the seventh century. The main analytical and interpretative tools used in this study are religious conversion and ecclesiastical competition. It examines sources discussing Nicene–Homoian encounters in Vandal Africa, Gothic and Lombard Italy, Gaul, and Hispania – regions where the polities of the Goths, Suevi, Burgundians, and Franks emerged. It explores the extent to which these encounters were shaped by various religious policies and political decisions rooted in narratives of conversion and confessional rivalry. Through this analysis, the aim is to offer a nuanced interpretation of how Christians in the successor kingdoms handled religious dissent and how these actions manifested in social practices.

The Introduction presents the main topic of the book – the role of conversion and competition between Nicene and Homoian churches in the post-Roman West – and the methods applied. It explains terminology (Nicene, Homoian), theorises the concept of conversion as a tool of historical analysis, and presents the purpose of the cross-regional comparison that follows.

The fourth century AD historian Ammianus Marcellinus remarked that “no wild beasts are such enemies to mankind as are most of the Christians in their deadly hatred of one another.” More to the point, the discussion of the nature of Christ drove a wedge within Christian communities in Antioch as elsewhere and ignited conflicts on a unprecedented scale. This chapter describes how the playing out of these debates had repercussions at all the levels of Antiochene society.

This chapter traces the fortunes of our modern understanding of ‘belief’ which is deeply informed by its original uses in a religious context. It begins with an account of faith/belief (Greek: pistis) in early Christianity, showing how the primary meanings of the term related to trust rather than intellectual assent. In the medieval period, this social component of faith/belief was formalised in the conception of ‘implicit faith’, which enabled lay believers to affirm abstruse theological doctrines without the requirement of a full intellectual comprehension of what was being affirmed. While it is possible to speak of the propositional content of belief during this period, the identity of the faithful was established more by liturgical practice than assent to doctrinal propositions.

The conclusion proposes alternative ways to think about Christian normativity, drawing on the concepts of polydoxy and religious autonomy from Alvin Reines, with additional support from Catherine Keller and Laurel Schneider, and the concept of theological disobedience, derived from Louis Michael Seidman’s notion of constitutional disobedience.

Oral witness is also the basis for the account of what Margery Baxter, charged with heresy at Norwich in 1428, has said and done. Her friends and neighbours are called to witness against her, and through their words we learn not only of the shocking things she has said which confirm her contempt for the Church, but details of the women’s lives.

The last fifty years have seen a considerable boom in the study of ancient book culture, reading and scribal habits. This chapter situates the present study in light of these scholarly developments and raises some critical questions concerning certain viewpoints that have been put forward regarding how to approach the Nag Hammadi codices given what is known about religious materiality in antiquity. In light of the latest scholarship on ancient literacy surveyed in this chapter, it is argued that the texts were most likely produced by and for the direct use of a small educated societal minority. The chapter also addresses some of the old and new scholarly paradigms and ideological setups in the scholarship on the texts: for example, the potential and limits of the trend called ‘New Philology’, as well as the problems attached to concepts like ‘heresy’ and ‘Gnosticism’ and their persistent connection with the Nag Hammadi collection.

Although entry into Islam is costless, exit was banned early on. According to a widely accepted interpretation of early Islam, soon after Muhammad’s death a precedent for banning apostasy was set. In fact, the underlying dispute was over zakat, and the episode amounted to enforcing the tax code. But recasting this historical detail would not necessarily settle controversies over Muslim religious freedoms. Certain Quran verses speak of retribution against nonbelievers. Others preclude compulsion, arguably establishing a right to leave Islam. Insofar as a textual inconsistency exists – and that itself is debatable – for advocates of liberalizing Islam the challenge boils down to prioritizing liberal verses. Blasphemy and heresy charges, used repeatedly to persecute heterodox sects, also restrict sundry liberties. The fear of getting accused of religious offense constrains political discourse and inhibits collective action. But a broadening of Muslim religious freedoms through the liberalization of apostasy and blasphemy rules is not unthinkable. Analogous transformations have occurred in other religions. Besides, Islam has been reinterpreted repeatedly since its emergence, radically so in modern times. Innovations include Islamic banks, which are business corporations, and various Islamic NGOs, which are organized as nonprofit corporations. Evidently, no absolute barrier exists to broadening Islamic religious freedoms.