Peter Cornelius Claussen’s Die Kirchen der Stadt Rom im Mittelalter 1050–1300 is a supplement to the author’s path-breaking book on Roman marble workers, Magistri doctissimi romani (Stuttgart: Franz Steiner Verlag, 1987). Magistri is the first volume of the ambitiously conceived Corpus Cosmatorum, the second volume of which is an alphabetically organized compendium of the “high medieval” churches in which the marble workers were active. The second volume has appeared to date in three parts: part 1, with entries on twenty-nine churches from S. Adriano to S. Francesca Romana (Stuttgart: Franz Streiner Verlag, 2002); part 3 (S. Giacomo alla Lungara to S. Lucia della Tinta [Stuttgart: Franz Steiner Verlag, 2010]); and part 2, the book under review. Unlike parts 1 and 3, part 2 is virtually a monograph, with 330 densely footnoted pages devoted to a single building, the cathedral, and 38 pages by Darko Senekovic on the baptistery, S. Giovanni in Fonte.

In its chronological focus and alphabetical format, the Corpus Cosmatorum complements Richard Krautheimer’s five-volume Corpus basilicarum christianarum Romae (Vatican City: Pontificio Istituto di Archeologia Cristiana, 1937–1977), the indispensable catalogue of Roman churches founded before 850. Despite their complementarity and frequent overlap, Claussen’s project differs from Krautheimer’s in fundamental ways. Krautheimer was an architectural historian with a gift for archaeology, and his Corpus collects and analyzes the documentary and physical evidence for the design and structure of Rome’s early Christian and early medieval churches. He was interested in typology and in the roots and meanings of architectural forms. Claussen’s chief interest is the Ausstattung, the furnishings and embellishment that made churches liturgically functional. To him, medieval churches are not autonomous formal or structural creations but stages for clerical and papal display. He is an art historian with a predilection for sculpture. As a supplement to Magistri doctissimi romani, the multi-part second volume of his Corpus is intended to contextualize the chancels, thrones, altars, pavements, tombs, and cloisters presented and analyzed in volume 1.

The methods and presentation of the two corpora are concomitantly diverse. Krautheimer worked mostly from primary sources, including the results of his own excavations, and his presentation is rigorously analytical. Reflecting a more copious state of scholarship and his own different objectives, Claussen’s approach is less empirical, more conditioned by secondary sources, and his presentation is more subjective and discursive. In this volume especially, the result is less like a work of reference than a book-length art-historical disquisition. In an ingratiating introduction he admits as much, maintaining that the objective truths traditionally expected of a corpus are unattainable and apologizing for trying the reader’s patience with lengthy passages in which he struggles to find his own position on debated issues. He wryly observes that the mounds of footnotes (1,420 in all) do not resolve all uncertainties but are a sign of their inevitable persistence.

Such demurrals notwithstanding, the chapter on the Lateran basilica is the most comprehensive and well-informed account so far produced of the cathedral in the period immediately after the turn of the first millennium. It is based on exhaustive research, including meticulous inspection of every inch of medieval fabric still to be seen in and around the basilica (witness Abb. 151, a fragment of a medieval colonnade in what is apparently a toilet) and a combing of photo archives in Rome and elsewhere (there are also many fine new photos by the author). Primary sources adduced by previous scholars have been scrupulously revisited and a few new ones are introduced (e.g., Abb. 60–61). As a result, the conclusions are fresh, even if the terms of the discussion are dictated by prior, arguably more original publications by Krautheimer, Ronald Malmstrom, Sible De Blaauw, Ingo Herklotz, and others.

Unlike other cathedrals in Italy, northern Europe, and England, the Lateran cathedral was not reconstructed or replaced in the period of Claussen’s purview. It remained the wooden-roofed column-basilica erected by Constantine immediately after 312, although the nave had been extensively rebuilt after collapsing in an earthquake in 896. Claussen’s text is accordingly devoted to additions and modifications to this persistent core: the east end of the nave (38–92); the apse and transept (92–167); liturgical furnishings, tombs, and other sculpture (184–254); and the cloister (254–315). Appendices contain a catalogue of the miscellaneous fragments in the cloister walks (many of which are patiently reassembled in the text in verbal reconstructions of important tombs and tabernacles), as well as a selection of “sources” transcribed from extant inscriptions and manuscripts, or in some cases from other publications.

The east face of the church was a composite, with the gabled end wall of the nave rising over the asymmetrical conjunction of a colossal trabeated portico and the blank wall of a tenth-century chapel perpendicular to the two south aisles. Claussen proposes a number of revisions to the prevailing views about these elements, arguing against Volker Hoffmann that the facade wall did not go back to Constantine but was a replacement sponsored by Pope Nicholas IV (1288–1292), and against Herklotz that the trabeated portico—signed by Nicolaus Angeli and thus datable to ca. 1180–1200—was not the work of an unnamed pope but an embellishment sponsored by the cathedral chapter of canons. This explains the clumsy combination of the grand portico and the decrepit chapel, as the latter was the papal sacristy, which the canons would not have had the jurisdiction to replace. It also means that the propagandistic inscription and mosaic scenes in the portico’s architrave were not papal statements of primacy (“I am the mother and head of all churches”), but a message from the chapter to a pope who tended to favor St. Peter’s. Finding Innocent III to be the most likely target of such a reminder, Claussen revises his own earlier dating and puts the portico around 1200.

At the west end, the apse and ambulatory pulled down in 1881 (Abb. 57) were well-documented constructions of Pope Nicholas IV, replacing, respectively, Constantinian and fifth-century originals. Claussen adds the towering transept to this campaign, convincingly refuting De Blaauw’s suggestion that it was erected in the twelfth century. Sixty-plus meters long and over 27 meters high, the transept is the largest-known construction undertaken in medieval Rome. With this attribution and the putative rebuilding of the facade, Nicholas IV emerges as the author of a grandiose modernization that encompassed both ends of the Lateran basilica while preserving its historic outline and the nave. Claussen sees the motive for this ambitious project in the pope’s Franciscan profession and interprets it as a literal realization of the frequently painted dream of Pope Innocent III, in which St. Francis saves the tottering Lateran from collapse.

Claussen’s profound and intimate knowledge of the cloister makes this section a particular pleasure to read. He knows every stone (and has counted them), and through sustained observation and description he extracts their history, including the underlying arithmetical design, the date (1225–1235) and order of construction, the number of masters (five, unless the two “imitators” were really one), and their role in realizing or modifying the program. Here as in other places Claussen revisits the conclusions of his own prior research, from which he maintains a remarkable objective distance. Along with some inevitable repetition, there is also much reconsideration and revision, as well as a shocking demonstration of the marble disease that has caused the sculpture to crumble within the span of his own engagement with it (Abb. 198). Scholars should be all the more grateful for his and Senekovic’s well-focused photographs of its memorable details.

Senekovic’s brief chapter on the baptistery provides an overview of its building history from the debates about its early Christian outline to the early modern era. There is relatively little to report from the period covered by the Corpus, but two primary sources vividly evoke the reality that mosaics and marble were meant to transcend. An ordo from before 1145 prescribes that while the consecrated water should remain in the old immersion font all year, some of it should be regularly drained off and replaced “so that it does not stink too strongly and bring shame upon the sacrament” (371, n. 62); similarly the vestibule should be treated with air freshener (herbis odoriferis) before high holidays so that celebrants passing through it will not be disgusted by the stench of the bodies buried inside (380, n. 109). Despite its atmosphere, the vestibule became an oratory with two new altars consecrated by Pope Anastasius IV in 1154.

This macroscopic summary conveys only the principal results of a book that really should be read microscopically. I have not touched on the liturgical furniture and tombs, nearly all postdating the nominal terminus of 1300, for which readers should consult the important review by Julian Gardner (Journal of the Society of Architectural Historians 69, no. 3 [September 2010]: 446–48). With its depth of detail and lengthy consideration of alternatives, Rome-centered to the point that even medievalists whose expertise lies elsewhere may find it hard going, this is a book for hardcore specialists. If I have a regret, it is that the volume does not provide an easily accessible account of the “mother of all churches” for readers who are not already familiar with the building. In compensation, however, scholars have a new milestone in the study of this eminently (self-)important basilica, the point from which all subsequent studies will have to depart.