No scholar interested in the history of Roman Christianity or the Catholic Church can deny the importance of the basilica of Saint Paul on the Via Ostiense. Built in the fourth century as a memorial to the burial of the apostle Paul, it has remained a focus of popes, emperors, and worshippers until it was nearly destroyed by fire in 1823. And yet, the basilica has remained relatively peripheral in studies of Rome and its church, especially when compared to buildings like Saint Peter's and the Lateran basilica. Nicola Carmelenghi's book is a welcome corrective to this oversight, a fundamental reference for anyone interested in the history of the building and its place in the life of the Roman Church. Rather than focusing on a particular phase or part of the building, the author narrates in impressive detail the long history of restorations, renovations, redecorations, and use of the church from its original construction to its destruction by fire. Making use of a wide range of sources, including archival material (often previously overlooked), drawings, archaeological reports, and different types of texts, Carmelenghi presents a comprehensive picture of this history, bringing new information and proposing new interpretations that correct previous misconceptions and assumptions. This is backed by the lavish use of illustrations, including a number of digital reconstructions (the making of which is discussed in a specific appendix).

The aims and methodology of the book are set out in the introduction: to narrate the history of Saint Paul's in the longue durée, integrating its changing architecture, the actions of its many patrons, and the changing meanings given to the building over the centuries. Carmelenghi starts with the prehistory of the site, when the Roman necropolis of the Via Ostiense was used to bury the remains of the apostle Paul (chapter 1). The site was monumentalized as a space for memory and worship with the building of a basilica during the Constantinian period—Carmelenghi suggests it was built by Constantine II and Constantius II, and not their father (38). The building was completely rebuilt on a much grander scale during the Theodosian period (386–410): the new transept alone was as big as the original basilica. This was an imperial monument, celebrating in its unified architecture and lavish decoration the political harmony and Nicene faith of the imperial family (chapter 2). The ensuing centuries saw a growing episcopal presence, a process started by Leo the Great (chapter 3). Making use of aristocratic and imperial patronage, Leo and his successors redecorated the church with signs of episcopal authority (including expanding the series of papal portraits that adorned the nave), built a presbytery that highlighted the status of the clergy, and included the building in the city's liturgical calendar through the stational liturgy. These first chapters set the background for the history of the basilica, indicating the different forces that shaped its appearance and function: the divide between liturgy and memory, between the original meaning of the building and the interests of patrons.

This became clearer when Saint Paul's was turned into the center of an important monastic community, whose priorities didn't always coincide with that of the papacy. Carmelenghi shows how vibrant the Carolingian period was (chapter 4), for as the monastic community gained importance, patrons sponsored the cult of relics and the parceling up of the basilica, and the threat of raids led to the building of a wall that made Saint Paul's a central point in Rome's defensive system. The presence of monks was at the root of the basilica's golden age from the eleventh to the fifteenth century, when it attracted renewed works and the physical presence of the monastic community was made more conspicuous by the initiatives of Roman families and the popes (chapter 5). The history of the basilica was marked by the oscillating fortunes of the Roman Church and of papal policies: following a relative decline in the fifteenth century, Saint Paul's was embellished and adapted to serve Sixtus V's (1585–1590) elaborate liturgical designs, only to see a greater monastic assertiveness after his death (chapter 6). The final phase of its history was marked by a greater awareness of its historical importance, as a symbol of the church's antiquity and of episcopal authority. Carmelenghi discusses how the concept of risarcimento (literally compensation), the restoration of a building and its features as they should have been, presided over the works carried out in the eighteenth century. This is highlighted in the epilogue, where the author shows how the destruction and the restoration of the basilica—including the debates surrounding it—were viewed through increasingly historical lenses, which still define the identity of the building today.

As a book, St. Paul's Outside the Walls is a starting point, and not the end of the conversation. In trying to weave together so many strands of physical, institutional, and religious history, Carmelenghi frequently touches on points that are not properly developed. This leads to simplifications: the importance of the apostle's memory and relics in Rome's religious life is surprisingly neglected, and the frequent mentions of liturgical issues do not lead to a proper discussion of how liturgy took place in Saint Paul's—in spite of the great attention paid to the decoration and furnishing of the church. Physical changes are thus treated as a series of initiatives by competing patrons that were only brought together by the fact that they took place under the same roof. The detailed discussion of the appearance and date of the most minute elements rarely leads to a coherent picture of what the basilica looked like, or of how it was used in any given period. These are all important points that will hopefully be explored by scholars in the future. With its wealth of information, references, and ideas, Carmelenghi's book will be the necessary point of reference for all of them.