The Cathedrals of Pisa, Siena and Florence

A Thorough Inspection of the Medieval Construction Techniques

Pietro Matracchi, Luca Giorgi

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9780429614842
• Edition: 1
• Topic: Social Sciences
• Subtopic: Archaeology
• Index: Social Sciences

The construction techniques and concepts of the cathedrals of Pisa, Siena and Florence are examined in detail, based on new data and using a methodological architectural diagnostics approach.

New detailed surveys, carried out using often advanced tools, together with direct and in-depth inspections to examine all parts of the buildings, have enabled us to identify the building phases and the different construction techniques used over time. The information thereby acquired also formed the basis for a new interpretation of the archival documents.

Accordingly, the problems encountered and the solutions adopted in the three cathedrals have been understood: in Pisa the construction of the elliptical dome above the rectangular crossing consisting of six thin pillars below; in Siena the design changes from the first system in the 13th century to the 'Duomo Nuovo', and the structural adaptations following earthquakes; the specific construction solutions adopted in Florence during the instability encountered in the construction of the large vaults of the basilican body.

The comparison of the three buildings in terms of architectural and construction solutions also revealed unexpected relationships between the construction events of Siena's Duomo Nuovo and the solutions then used in the large basilican body of Santa Maria del Fiore.

The methodology employed has led to an understanding of the actual structure of the three cathedrals, an essential basis for a correct evaluation of the state of conservation of the churches for any restoration work.

The book is aimed at scholars of architecture and ancient building structures, graduate and postgraduate students, and architects and engineers who plan architectural conservation and strengthening works for historical buildings.

Chapter 1
Introduction

Medieval cathedrals have always sought to represent the maximum architectural expression of the cities in which they stood, all the while seeking to rival similar buildings in other places.

The extraordinary characteristics of cathedrals in terms of the richness of materials and the drive to come up with innovative architectural solutions made for an extremely complex construction, which generally lasted for centuries.

While they were being built, there was no supposed original design to follow which would have provided all the necessary information; rather, the key decisions on the choice and production of the materials and the constructive solutions were made at the construction site itself. Furthermore, decisions about the architectural structure to be created were often made step-by-step during the execution phases, often demonstrating a willingness to make changes that were capable of calling previous choices into question. The construction site was a place where architectural experimentation occurred.

All these aspects emerge strongly from the studies conducted on the cathedrals of Pisa, Siena and Florence presented in this book. The research results were obtained through architectural diagnostics based on a direct accurate analysis of the structures and an interpretation of the surveys, conducted with traditional techniques and laser scanners. In this latter case, the data provided by 3D modelling was processed to obtain the diagrams, sections and elevations deemed necessary to understand the real, authentic structure of these churches. The architectural diagnostics carried out led to the observation of specific aspects of these buildings without losing sight of their general architectural context, and when the general structure was taken into consideration, we also contemplated the multiple specificities linked to an extremely complex building structure, where countless contributions have become stratified over the centuries.

Whenever possible, the information was supplemented with the results of non-destructive or moderately invasive instrumental investigations, such as thermographic imaging, dendrochronology, the laboratory analyses of mortars, ground-penetrating radar, flat-jack tests, core drilling, measuring the tensional states of metal ties and information on the structure of the subsoil. Other data were obtained from structural modelling, available for the dome of Siena cathedral, and for the transversal openings of the basilican body of Santa Maria del Fiore.

The studies conducted an in-depth analysis of the complex construction genesis of the cathedrals, considering the operational conditions faced by the builders at these construction sites. The information obtained from a similar approach was consulted in relation to archive documents, in many cases giving rise to new interpretations more pertinent to what actually occurred at the construction sites and the works they refer to.

This research based on architectural diagnostics had two main purposes. One was to learn more about the construction history and transformations of the cathedrals of Pisa, Siena and Florence. The aim was to cast aside idealizations by paying constant attention to the concrete elements – the materials, construction solutions and state of conservation – making up these buildings of extraordinary cultural value. The genesis of these churches has a multifaceted character and involved many builders and the development of several designs that accompanied the work. The other fundamental goal was to provide appropriate knowledge in order to understand and address the conservation problems of such complex buildings, above all regarding the constructive structural aspects. Each of these churches, beyond their apparent homogeneity, is in fact characterized by many construction aspects, which have sometimes changed significantly over time, knowledge of which becomes vitally important when it comes to assessing any structural vulnerabilities. It should be pointed out that the vulnerabilities are rarely the result of a systemic condition and are more frequently linked to specific local situations, caused by particular episodes. Precisely due to their specific character, in order to identify local vulnerabilities, an accurate diagnostic study commensurate with the specific characteristics of the building is required.

This book is divided into three chapters, each dedicated to one cathedral. The areas covered in each chapter follow the course of events and are placed in chronological order.

In Pisa cathedral, the transept was studied, and in particular, the complex system of construction solutions used in the transition from the rectangular crossing to the elliptical plan of the dome above. In the drum area, a surprising variety of construction systems were identified, which allowed the builders to gradually create a connection between the crossing and the dome. In addition to the pendentives, a set of overlapping arches were created, in some cases skewed and partially overhanging; walls were built with variable inclinations, and in some cases, the archivolts of the arches were also raised following inclined planes. The complex relationship between form and structure was confirmed by the detailed analysis of the masonry structure of the pendentives, documented for the first time with extremely accurate surveys, the forerunner of which was Piero Sanpaolesi (1975). Among the apparently similar pendentives, significant differences were detected in the masonry, reflecting the gradual definition of the construction solutions developed at the site during the execution phases. The stability of the crossing is also ensured by the use of flying buttresses with two archways, placed next to the transverse arches of the crossing, the existence of which in the false ceilings of the matronea was noted for the first time by Adriano Peroni (1995, 49–50).

Siena cathedral is perhaps a unique example for the continuous innovative drive to alter projects that were in progress or architectural arrangements that had already been completed. On these events, a long and in-depth study campaign promoted by Peter Anselm Riedl and Max Seidel, published in several volumes on the surveys (Haas & von Winterfeld, 1999b), the architectural analysis (Haas & von Winterfeld, 2006a, 2006b), and the archive documents (Giorgi & Moscadelli, 2005), marked a turning point. The topic was resumed with new surveys and studies, placing particular attention on the medieval construction sites that led to the construction of the intermediate cathedral in the sixth decade of the 13th century, and the events of the “New Cathedral” which concluded with the unfortunate outcome of its collapse due to the inadequacy of the construction solutions put in place.

The Santa Maria del Fiore complex – made up of the baptistery, cathedral and bell tower – was the subject of an extensive and complex programme of studies and surveys promoted by Giuseppe Rocchi Coopmans de Yoldi, published in four folio volumes (Rocchi et al., 1988; Rocchi Coopmans de Yoldi, 1996, 2004, 2006) containing contributions from the authors of this publication. In this volume, attention has been placed on the cathedral construction site, starting with the renewal of the ancient cathedral of Santa Reparata at the end of the 13th century, followed by the construction of part of the façade and the flanks of the present-day cathedral and a subsequent period when work came to a standstill, during which most effort was concentrated on the construction of the bell tower, which was then completed with the contribution of Giotto, Andrea Pisano and Francesco Talenti. As regards the cathedral, 1357 was a year of great changes which led to the creation of a vaulted basilican body with a central nave with four bays, with an average centre-to-centre distance between the pillars of 19.60 m. The exceptional nature of this construction dimension required, in addition to the use of flying buttresses hidden in the garrets of the side aisles, the preparation of temporary works that guaranteed the stability of the structures during construction. So the central nave was fitted with temporary ties, the last of which were removed in Brunelleschi’s time, while other similar ties with a temporary function, placed in the garret areas, were not removed.

In large buildings with vaulted systems, the problem of stability during construction was cogent in that very different static conditions were gradually obtained with respect to the final constructive structure. This is a highly interesting aspect of the construction work, but there are still few studies on it. Temporary ties were also placed in the central nave of the cathedral of Majorca (Roca et al., 2019, 160–161), which has rectangular bays but of a similar width (19.40 m) to those of Santa Maria del Fiore.

Interaction between the constructed parts and the parts under construction had significant consequences in the layout of Santa Maria del Fiore. When the construction of the dome reached the second corridor, that is two-thirds of its vertical height, there was subsidence in the pillars of the dome adjacent to the basilica body. This resulted in instability in the fourth bay of the central nave, traces of which can still be seen today. It was Brunelleschi himself who came up with the idea of the present-day double ties crossing the central nave and that, with wooden elements, continue into the garrets of the side aisles anchoring to the pillars of the flying buttresses. Brunelleschi also made changes to the flying buttresses between the second and third bays, adding small arches in an intermediate position to the pillars, thereby creating double level flying buttresses. This intervention was a big change with respect to the work of the medieval builders, who had wanted to construct the central nave without ties.

Much more incisive alterations were made on several occasions to the structure of the Siena cathedral, which was completed in the 14th century. In this case, it was the vulnerability of the structures brought to light by the numerous earthquakes that led, from the 16th to the 19th centuries, to a gradual but unstoppable conceptual rethinking of the entire constructive structure, which saw ties, buttresses and flying buttresses placed in the aisles. These were all constructive protections that the medieval builders had chosen not to use.

Another issue examined is the correlation between construction phases. In 1357, Francesco Talenti and Benci di Cione were called to Siena as consultants to give an opinion on the critical conditions of the “New Cathedral,” which then collapsed a few months later. The two builders must have learned a great deal from this experience. At the same time, in Florence, it was decided to finish the construction of the bell tower, interrupting an additional level in order to begin building a vaulted basilican body considerably larger than that of the “New Cathedral.” Benci di Cione, and Francesco Talenti in particular, played a leading role in this new start to the Florentine cathedral.

Chapter 2
Pisa cathedral

2.1 From the rectangular base of the crossing to the elliptical springer of the dome: architecture, building site and constructive solutions

As is the case for many buildings from the same era, documentary evidence on the origins and construction of Pisa cathedral was often incomplete or entirely missing. The 5-aisle basilican body, which extends beyond the crossing up to the semi-circular apse, and the arms of the 3-aisle transept joining the space surmounted by the dome are thought to be the result of complex building work started in the sixth decade of the 11th century and completed in the 1380s (Peroni, 1995, 14–15) (Figures 2.1 and 2.2)

Figure 2.1 Pisa cathedral; view of the façade and north side.

Figure 2.2 Pisa cathedral; view of the transept.

The epigraphic evidence found in the cathedral is particularly important, recognizing the key role Buscheto played in the preparation of the project. He was succeeded by the master Rainaldo and thereafter by other builders. The cathedral was consecrated and was the seat of the Council in the presence of Innocent II in the first half of the 13th century (Ronzani, 1996, 35). The existence of the southern transept was also confirmed in this same period. The bronze door of the façade was built in 1181, which would seem to imply the completion of this part of the building. However, archaeological evidence was found that suggested there had been an extension to the west of the aisles and therefore that the basilican body was originally smaller (Bacci, 1917, 2; Scalia, 1982, 817–859; Milone, 2008, 73–74, 78). Work continued on the dome until the 1380s (Tanfani Centofanti, 1897, 439–442) (Figure 2.3)

Figure 2.3 Nave and apse of Pisa cathedral.

In addition to the complexities of the building phases, transformations occurred which over the years have changed the structure of the church several times. An extremely important one was the fire in 1595, which destroyed a large part of the building and resulted in the consequent restoration of the wooden parts of the roof, as well as stone elements like the capitals (Peroni, 1995, 120).

The architecture of Pisa cathedral is an extraordinary complex subject. It is examined here through in-depth studies, in particular concerning the specific construction solutions of the domed space, considered in the inseparable relationship between architectural space, structure and the act of building (Figures 2.4 and 2.5)

Figure 2.4 Laser scanner survey of the external area at the level of the roof of the aisles.

Figure 2.5 3D model of the laser scanner survey inside the drum.

The rectangular crossing is formed from the intersection between the five-nave basilica and the three-nave transept. The central nave of the longitudinal part of the building determines the width of the shorter side, while the longer side extends for the full width of the aisles of the transept (Figure 2.6).

Figure 2.6 Plan of the transept and crossing.

On the four corners of the crossing, there are cruciform pillars, which on the shorter side support pointed arches that extend for the full width of the nave. These arches are of different heights, and the one facing the basilican body is higher. On the longer side of the crossing, there are two monolithic granite columns placed in continuity with those of the nave of the transept. Those of the crossing, however, have a larger diameter, equivalent to that of the column of the central nave, measuring approximately 1 m (Figure 2.7).

Figure 2.7 Longitudinal section of the transept.

The rectangular space within these bounds is regular, with almost equivalent opposite and diagonal sides. The new surveys instead highlight a unique characteristic of the transept arms: they have two orthogonal sides, the east sides with the respective end walls with apses and the western sides which become narrower as they approach the crossing gradually reducing the width of the adjacent aisles. In particular, the walls just mentioned are rotated 1° in the north arm and 2° in the south arm. In the latter case, in the west aisle, the gradual narrowing in the first four bays is particularly marked, reaching a maximum of around 45 cm.

A similar alignment of the transept arms would suggest that the construction of the entire three-nave part of the building was not coeval and that the positioning of the western wall depended on the dimensions of the crossing. We wanted to emphasize this aspect to demonstrate how complex the construction of the cathedral may have been, even if the purpose of this work was not to identify the construction phases of the ground plan.

The accentuated longitudinal development of the rectangle inside the crossing, roughly 12.50 m wide and 17.20 m long, stems from specific constructive relationships with the adjacent parts of the building. The cruciform corner pillars are aligned transversely with the sides of the transept and longitudinally with the arches corresponding to the central nave.

The intermediate columns on the longer sides of the crossing are aligned with those of the...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Table of Contents
• Series editor foreword
• Acknowledgements
• About the authors
• Chapter 1 Introduction
• Chapter 2 Pisa cathedral
• Chapter 3 Siena cathedral
• Chapter 4 Florence cathedral
• References
• Index of names and places
• Index of subjects