This passage from Eusebius of Caesarea’s Ecclesiastical History, written at the start of the fourth century, is a classic account of the origins of heresy within Christianity.2 Drawing on the now lost second-century Memoirs of Hegesippus, it begins in Jerusalem with a “pure,” undivided community of the faithful. Soon, however, dissension arose through the figure of Theboutis, who brought in external ideas from the seven “sects” of Judaism and began the process of corruption: more heresiarchs arose and founded more heresies, which were named after them, and these in turn begat further heresies and dangerous doctrines, together with false figures of authority, as had been foretold in Scripture. From these beginnings, therefore, heresy grew and multiplied in opposition to an unchanging orthodoxy, with every individual and group innovating in such a way that their views differed not only from the true Church but also from each other, while nonetheless forming part of a network of heresy stretching back to a shared origin. In this one example, it is already possible to identify many of the essential features that would go on to characterize heresiological rhetoric, especially in some of the more elaborate forms it would take in the post-Constantinian world: a focus on doctrinal deviation from an established norm; the pernicious influence of inappropriate “external” ideas imported into Christianity; the assigning of blame to named heresiarchs with questionable motives; the organization of opponents into discrete groups, frequently named after their supposed founder and thus separated from the name of “Christians”; and the tracing of genealogical links between heretical sects, allowing each one to be tied to others and thus damned by association, while also contrasting the manifold disagreements of the various groups with the singular, unchanging faith of the Church.3