This is a book to be read backwards. The reader should start from its very rich bibliography, appreciating the amount of learned scholarship that has developed across decades on minorities and foreign communities in early modern Rome. This compilation is a treasure trove of learning, especially on what are now known as the Catholic Churches sui juris; but that is only the first of many reasons to be thankful to the editors for their impressive work. Subsequently, on reading the introduction, it becomes clear that the volume does much more than simply systematising the knowledge that has been accumulated on minority groups that lived in Rome between the fifteenth and the eighteenth century. In this sense, the book is not simply a ‘companion’: actually, it is a fresh retake on the entire matter. This is not just the recounting and updating of the stories of Greeks, Arabs, Syrians, Maronites, Armenians, Ethiopians, New Christians, Muslims, Jews (and even the occasional Protestant) who lived, travelled or were enslaved in early modern Rome. Instead of looking at these figures from Rome's point of view, as has often been done, the book endeavours to start from their own experiences in the Eternal City, from why they went and stayed there, and how they dealt with the authorities of the Urbe. In sum, this is not a new history of uniatism with Jews and Muslim added to it – but much, much more.

Firstly, the book builds on the current historiographical trends on early modern religious identities, and on the negotiated nature of devotion and religious belonging. As has been written many a time, conversion in particular is often an horizontal affair, made of compromises and of enmeshment, of mixing up practices and of new creative identities, something most evidently visible in many ‘peripheries’ (but in this case at the very heart of Europe), where old and new devotional practices co-inhabited, in a juxtaposition that was often far from a replacement of the old with the new. This way of looking at minorities and at their integration in the city is very much interwoven in all the book's chapters. The volume adopts a very fluid definition of ‘minority’: not simply those who did not conform to Catholic practices (like Jews and Muslims), but also those who became Catholic having been born within another faith's fold, like the New Christians. On top of this, the volume devotes ample attention to two better-defined minorities: to the Catholic-Jewish interactions in the city, not least with a stimulating chapter by Emily Michelson on the sermons that representatives of the Jewish community were regularly forced to listen to; and to Muslims, with a granular analysis of slavery in the port of Civitavecchia, where enslaved ‘Turk’ labourers were to be found until the early nineteenth century, thanks to a chapter by Justine A. Walden.

In this volume, Rome appears as an ambivalent city. On the one hand, it is the centre of the universalist dream of the Counter-Reformation papacy, focus of the representation of self in what Simon Ditchfield has labelled as the making of ‘the myth of early modern global Catholicism’. Therefore, as the chapter by Mayu Fujikawa illustrates, the way in which the pope welcomed foreign ambassadors changed profoundly according to their own religious identity: even in the case of legations from Persia, Japan and Siam, through ritual and political theatre, the centrality and superiority of the papacy was constantly reasserted. Also part of this were the institutions that actively sought the conversion of travellers, like colleges and hospitals, here in particular studied by Irene Fosi. But – as Matthew Coneys Wainwright points out – these were much more ambivalent and much less successful than historiography has previously assumed.

On the other hand, this book shows an early modern Catholicism that was not a global religion in the making, but very much an inter- and intra-religious enterprise on the ground, with all its messiness and contradictions. Rome in this book is not caput mundi, but – as the editors explain – just a multi-layered complex city. This is particularly true of pilgrims and travellers from Armenia, Syria, the Holy Land and Ethiopia. Albeit progressively ‘normalised’ and integrated into the Catholic flock, these communities brought with them an alterity that Rome constantly tried to re-negotiate. But, wisely, the book looks at the complexity of individual itineraries, and does not reflect on these communities only in terms of ‘nations’, as if ethnic and religious identities were a monolith. Chapters by Sam Kennerly, Olivia Adankpo-Labadie and Cesare Santus deserve to be particularly commended not only for their learning on the lives of Eastern Orthodox travellers and pilgrims, but for adopting their point of view in the understanding of early modern Rome. It is an approach also shared by Serena di Nepi, in her elegant reassessment of the issues concerning slavery and conversion in the papal states.

This book is a ‘companion’ not just because it defines the state of the art on the issue of early modern religious minorities in Rome, but because it will really ‘accompany’ any further research into this topic. It is a map, and in a very real sense: it will be impossible for the reader to visit Rome again and not want to go to some of the many churches here discussed, including to the Armenian and Maronite congregations. But most of all, to the church of St Stephen of the Abyssinians that – tucked away in the Vatican behind St Peter's Basilica next to the Teutonic cemetery – really is a hidden treasure.