When I was in my first semester of graduate school, I was presenting on the church of San Vitale in an art history seminar. The professor was a long-tenured member of the faculty and an expert on Byzantine architecture. The first words I uttered were the “Basilica of San Vitale,” which met a swift rebuke from the professor, correcting me that San Vitale is not a basilica as it does not follow a typical three-nave or five-nave basilica plan. Instead, its plan is octagonal and thus should be called a “church” rather than a “basilica.” From that point on, I never made the same misstep in identifying San Vitale again, but I was always curious about the place of an octagonal church plan in the history of Christian architecture. Mark Johnson has filled that curiosity with his latest book that situates San Vitale in the broader array of cognate churches in late antiquity. Johnson attempts to answer why the octagonal plan was implemented, what was its significance, and how common or unique is San Vitale is in adopting an octagonal plan. To answer these, Johnson places San Vitale in a wider study of prior churches and martyria in late antiquity and concludes that octagonal-plan churches are certainly unique in Christian architecture.

Mark J. Johnson is professor of ancient studies at BYU and has published in the field of art and architecture of late antiquity. While San Vitale is seemingly the focus of this work, Johnson places San Vitale and SS. Sergius and Bacchus in Constantinople (the church most often compared to San Vitale) in conversation with thirty-four other octagonal-plan churches he has identified. Johnson organizes his study chronologically, beginning in the fourth century and proceeding chapter by chapter to reach the era of San Vitale in the sixth century. Beginning with the fourth century, Johnson provides space for discussion of octagonal-plan structures. As many of these from the fourth century are either recently excavated or in ruins, Johnson must rely upon excavation reports and mentions of the structures in primary texts. Obviously, structures that are more notable receive more attention due to the existing evidence. For example, his treatment of the first octagon used in Christian ecclesiastical architecture at the Church of the Nativity in Bethlehem utilizes a blend of art historical sources and primary texts such as Jerome, Paulinus of Nola, and the Bordeaux Pilgrim's account. Similarly, Constantinian churches rely upon Eusebius's Vita and many other patristic sources, making Johnson's treatment a useful resource for cataloguing patristic mentions of sites such as the Great Church in Antioch.

While the material on many of the thirty-four churches Johnson identifies is useful, some entries are briefer than others, making these early chapters read more as a catalogue or detailed encyclopedia entry on octagonal churches (still, this does not detract from the value of this study). Johnson's discussion progresses in detail as he treats the Justinian octagonal churches such as SS. Sergius and Bacchus, leading to his penultimate chapter on San Vitale. Johnson's treatment of San Vitale focuses on the historical context of its construction, the architectural design of the church, and brief treatment of the mosaic decoration on the interior. Johnson contributes a significant point by claiming that most scholars compare San Vitale to SS. Sergius and Bacchus by focusing on their differences rather than their similarities. Based on Johnson's calculations, the unit of measurement used at San Vitale was the “Byzantine” foot (.32m) rather than the “Roman” foot, a distinct similarity to SS. Sergius and Bacchus. Moreover, Johnson's study points out that octagonal-plan churches are constructed in the martyrium tradition of sacred buildings that became rare in late antiquity. Thus, San Vitale is one of the last of this type, particularly since relics of martyrs were more likely to be transferred to churches rather than to have a specific martyrium-type building construction on the site of the relics. Johnson concludes that San Vitale fits into church architecture under the era of Justinian's patronage, but San Vitale is still unique as it builds upon past martyria and inaugurates the construction of domed churches into the Byzantine era.

This book provides a strong contribution in the field of Christian architecture of late antiquity despite some drawbacks. Its primary contribution is serving as a resource for descriptions of octagonal-plan churches of late antiquity as well as cataloguing patristic references to these churches. The book is much weaker on analysis of these churches, including analysis of San Vitale, the primary church under discussion. The symbolic importance of the octagon and its significance in pagan and Christian resources is identified and discussed, but this treatment could be placed towards the beginning of the book to allow the reader to better understand the significance of these structures in context. The description of the iconography and mosaic plan of the interior of San Vitale is not Johnson's focus, as he admits. However, since he opens this door, the section on mosaics of San Vitale could be amplified, include more recent literature, and contain more robust analysis. While the case is strongly made for the significance of the octagonal-plan to martyria, a larger discussion of the relationship to baptisteries and the rite of baptism in the early church is warranted. The connection between martyrdom and baptism is explicitly made by authors such as Cyril of Jerusalem, who began to interpret Paul's letter to the Romans (chapter 6) of dying and rising with Christ as the heart of the baptismal liturgical drama (occasionally done within an octagonally shaped font as in Ambrose's Milan).

These shortcomings notwithstanding, Johnson's work is one that will be consulted by scholars of art and material culture of late antiquity, specifically for his attention to detail in the description of the fourth and fifth-century octagonal-plan churches he describes with patristic references. His book also contains a wonderful section of exquisite color plates of the churches he catalogues, adding to its value. One curious but rather glaring error stands out that is not likely the author's fault but the publisher's: the word “octagonal” is misspelled in the title and in subsequent title pages as “octogonal.” As the author never uses this spelling in his text, it seems this is due to a mistake of a German publisher working with an English manuscript. While minor, and probably explainable, its appearance on the cover it mars an otherwise strong piece of scholarship.