1This engaging book studies the representation of mystery cults by Christian authors from the second to the fourth century. It has a double aim. On the one hand, it chronicles how Christian authors construct mystery cults as a single phenomenon that for them defines contemporary paganism. This Christian picture is responsible—through much later mediation of course—for the modern scholarly idea of mystery cults as a particular and distinct phenomenon in Greco-Roman religion. On the other hand, F. Massa argues for the impact of mystery cults on Christianity. He builds on the insight that mystery terminology had spread widely among cults in the Roman Empire and into other areas of ancient culture, such as philosophy. Whilst the term mysterion was also biblical and used in the Septuagint, mystery cults were highly visible in contemporary culture and an element of Greco-Roman religion that early Christians competed with for followers. Christian engagement with mysteries was janus-faced: they could draw on mystery language, which conjured up a suggestion of deep truths, but also use it to decry pagans and heretics, suggesting that mysteries were the most pernicious core of a depraved religion. Ten chapters, organised along geographical and temporal lines, take the reader on a tour d’horizon of the Roman Empire. The range of sources surveyed is wide and F. Massa does a good job of bringing Christian texts in dialogue with their contemporaries and showcasing the variety of uses to which mystery cults and languages could be put. I liked in particular the chapter on the emperor Julian, showing how his supposed initiation in mystery cults is the result of a projection by his pagan admirers and Christian detractors. Chapter 10 on the end of Eleusis shows well how fourth-century Christianisation had little impact on the sanctuary and that fourth-century pagans attributed its demise to ritual impropriety and the accumulation of priesthoods by the last hierophant. If the book thus will be of much use to those interested in the spread of mystery terminology to Christianity and Christian representations of Greco-Roman cults, it seemed to me that it succeeds much better at showing the role of mystery cults in Christian discourse than their role in ritual competition. F. Massa intends to show that Christians competed with mystery cults and that this had an impact on the development of Christian communities and on Christian liturgy. I am not convinced of the usefulness of the concept of competition as Massa defines it, that is, as forms of interaction between religious groups in which each group tries to establish its difference with the other (p. 31). This seems to me to stray too far from the common sense understanding of competition, which implies a striving for superiority and attempts to increase one’s following, to be really helpful. Whilst it is important to ask, as Massa does, what the religious landscape was in which Christians functioned, that landscape cannot be simply extrapolated from Christian polemics, given the stereotypical nature of anti-pagan polemics in Christian sources. Hypothesising functioning mystery cults in Milan to account for references to these in Ambrose’s writings (p. 294) seems a bridge too far. Massa does not succeed in showing any impact of mystery cults on the liturgical development of Christianity and the points of contact alleged are slight (p. 53, on Meliton of Sardis focuses on a single word. I note in passing that the interpretation of Meliton’s On Easter on p. 48 seems to miss the anti-Jewish typology that shapes the text). There is also little or no engagement with scholarship on the history of liturgy. For the Confession of Cyprian, Massa shows well how its catalogue of mysteries is in line with earlier apologetics, so I fail to see why it nevertheless should represent fourth-century realities (p. 234). A further argument against this idea is that in the text the mystery cults occupy the lowest spot on a ladder that via astrology and magic climbs to philosophy. It seems that F. Massa himself is aware of the weakness of the case for competition, for the conclusion is more circumspect regarding the link with liturgy than some of the chapters (p. 347). Moreover, competition with mysteries is now emphasised to be a discursive invention of Christians (p. 348), more than a reality on the ground—which is indeed what the material gathered so well by F. Massa suggests. In sum, this book will be of much use to historians of the early Church, ancient religion, and philosophy, offering an enviably wide view on what mysteries were according to Christians.