How is the Tower of Pisa? After 850 years, its condition is excellent

Nearly a year ahead of the date of anniversary number 850 of the laying of the cornerstone of the Pisa Cathedral Bell Tower, famous throughout the world as the Tower of Pisa, whose construction began on August 9, 1173, the committee that will organize and manage the celebrations of the event has officially been formed. The committee, chaired by Pierfrancesco Pacini, president of theOpera della Primaziale Pisana, and under the honorary chairmanship of the archbishop of Pisa, Monsignor Giovanni Paolo Benotto, and the mayor of Pisa, Michele Conti, is the brainchild of Paolo Castaldi, consultant and sales manager, and the strategic impulse of Leonardo Ristori, marketing manager and journalist, which the Opera della Primaziale Pisana has welcomed by joining with full involvement.

The committee is composed of Patrizia Paoletti Tangheroni, Olivia Castaldi, Sara Pirola, Marcello Lazzeri, Stefano Maecenas, Laura Meoli, Gianluca De Felice, Pino Toscano and Antonio Schena. The committee will manage the anniversary celebrations by taking care of the decision-making and executive aspects, with the propositional and advisory support of a technical-scientific committee with the participation of Professor Nunziante Squeglia (Department of Building Engineering, University of Pisa), Professor Fabio Beltram and Professor Giulia Ammannati (Scuola Normale Superiore), Professor and Rector Paolo Mencarella and Professor Chiara Bodel (Department of Computer Science, University of Pisa), Professor Massimo Dringoli (Building Heritage Councilor), Professor Stefano Renzoni (art historian and writer), Giuseppe Meucci (journalist and writer), Professor Gabriella Garzella (Department of Civilization and Forms of Knowledge, University of Pisa), and Professor Diego Fiorini (art historian).

The committee was presented this morning in Pisa, at the Toniolo auditorium, as part of a conference taking stock of the condition of the Tower of Pisa: Claudio Viggiani, who provided information on the state of the monument, Donato Sabia , who focused on the issue of monitoring, Nunziante Squeglia , who took stock of the updated instrumentation, Marica Mercalli and Paolo Iannelli , who spoke about the Extraordinary Plan for Monitoring and Preservation of Cultural Heritage, and Roberto Cela and Anna De Falco , who instead spoke about satellite monitoring, were the speakers on the condition of the Campanile. Introducing the proceedings were Pierfrancesco Pacini and Salvatore Settis, president of the Campanile Surveillance Group.

It emerged from the monitoring that the Tower of Pisa enjoys an excellent state of health: the Tower, as well as the other buildings in the Piazza del Duomo, are the subject of constant attention, thanks to monitoring tools that allow experts to accurately assess their condition. In particular, after the 1999 under-excavation operation, by which the Tower of Pisa was effectively “straightened” by 460 millimeters, the movement of the Campanile was stabilized. The international committee coordinated at the time by Professor Michele Jamiolkowski, of which Salvatore Settis and Claudio Viggiani were members, and of which Nunziante Squeglia was an important operational arm, demonstrated that this sub-excavation brought the Campanile to a condition of absolute safety with respect to the phenomenon of instability of equilibrium from which it was suffering. In fact, over the past 23 years, the Campanile had continued to “right itself” with a very slow and progressively slower motion. The committee’s intervention had decreased the overhang by about 40 centimeters, to which another 4 centimeters or so were gradually added. And so, the health of the Bell Tower continued to improve.

Currently, the Tower, along with the Duomo, Camposanto and Baptistery, is the focus of a framework agreement between the Ministry of Culture, the Opera della Primaziale Pisana and the University of Pisa, signed last May, which provides for the development of forms of collaboration to put in place the conduct of activities of study and research related to the terrestrial and satellite monitoring of the buildings of the Field of Miracles and the city walls, and its combined use with archival data aimed at assessing and managing the risks to which they are subject.

The agreement is part of the broader “Extraordinary Plan for the Monitoring and Preservation of Immovable Cultural Heritage” adopted by the Ministry of Culture after the Genoa bridge collapse: the Plan reiterates the inspiring principles of the Cultural Heritage Risk Charter, drawn up in the early 1990s by the Central Institute for Restoration, to promote the active and conscious management of cultural heritage based on knowledge of the heritage and the risk to which it is subjected. The ultimate goal of the Plan is safety and conservation to be implemented through prevention, risk reduction and minimization of interventions on the heritage.

The Cathedral Square is one of the sites where monitoring has been in place for some time: under the framework agreement, terrestrial monitoring with traditional tools will be joined by satellite monitoring that uses satellite data to recognize the deterioration of artifacts and degenerative phenomena. There are currently several cornerstones for leveling measurements in Cathedral Square, mostly concentrated around the Tower: available elevation leveling data have been present since 1927. In particular, precision leveling was conducted by the Istituto Geografico Militare until the 1980s, then by the Politecnico di Milano until 2012, and then by the University of Pisa. The monitoring system is also installed on the shaft of the Tower: these are measurements to control the inclination and predict future trends, also with a view to safeguarding against structural problems.

The protocol implementing the agreement now includes two main activities: the comparison of terrestrial and satellite monitoring, and the establishment of an integrated monitoring system. The comparison will take place on Cathedral Square, and the establishment of the integrated monitoring system will involve the entire historic center of Pisa. The comparison between terrestrial and satellite monitoring will be implemented in two phases: a first one of comparison with historical satellite data, reconstructed from images since 1992, and historical data from terrestrial instruments. The comparison will then also take place in real time, with new terrestrial and satellite measurements simultaneously (company in charge of satellite processing is NHAZCA, a startup of Sapienza University of Rome, while terrestrial processing will be handled by Eurotec of Pisa). The terrestrial measurements will be obtained from an automated precision total station, which will be used until the end of the project. At the moment, the Opera della Primaziale is busy installing instruments that will allow for real-time comparisons: from corner reflectors (metal devices capable of stable and permanent reflection of the satellite signal) to reflective prisms. The establishment of combined monitoring, which is a more difficult objective to achieve, requires knowledge of the potential of the satellite system and awareness of the structural behavior of each artifact with its criticalities, in order to be able to identify the quantities to be measured, the range of values of interest and the values indicating critical situations. Informed geometric models of the artifacts and computational models, each with specific purposes, will be used for this objective. The geometric models will be used to organize the information and make a synthesis (e.g., by georeferencing the building elements), while the computational model will be used to provide indications of the health of the structures and enable predictions of operation in different and future situations. The Opera is also experimenting with new nondestructive diagnostic methods that will be able to provide information on the deformational state of the structures, and new methods of representation that will make it possible to synthesize in a single model all the information and data of interest for understanding the structural behavior of monuments. Thus, the project will also be an important research opportunity, as well as an opportunity to better understand the monuments in the square with a view to ensuring their safety.

“The memory of that Jan. 6, 1990, day when the Bell Tower was closed, seems distant today because of the time that has passed and because now daily hundreds of tourists from all parts of the world climb the three hundred steps that lead from the base to the top of the belfry,” says President Pacini. “Even more distant and outdated are the feelings, anxieties about the very difficult and courageous choices and liberating emotions experienced during years of intense study and work alongside the last international committee for the preservation of the Tower, the 17th, chaired by Professor Michele Jamiolkowski. This committee, over the course of more than ten years, has achieved a goal that seemed impossible to achieve and, by reducing the inclination of the Bell Tower by about 1900 arcseconds, corresponding to a decrease in the overhang of the seventh frame from the foundation plane by as much as 460 millimeters, has restored our famous monument to its pre-existing conditions dating back to the early 19th century. Our gratitude and admiration and that of the entire scientific and cultural world for this achievement, and especially for the manner in which it was achieved, are to be attributed to the characteristics of an intervention that, despite the dramatic nature of the conditions around it, solved the problem without in the least altering the characteristics of the monument, with absolute respect for its uniqueness and originality. Today, restored to a stable condition, the Tower is still under control through a surveillance team, chaired by Professor Settis and composed of Professor Viggiani and Professor Sabia, which has the delicate task of monitoring its movements. Therefore, it was an opportunity to talk about its state of health and, almost a year in advance, to begin the celebrations of the 850th anniversary of the laying of the foundation stone and for this to announce the establishment of a special committee, born spontaneously from the will of a number of Pisan citizens, supported by a prestigious scientific committee, that will organize the celebrations of this event, initiating all initiatives deemed useful and appropriate, in agreement with city institutions, such as conferences, exhibition events, concerts, initiatives with schools and universities, and literary competitions. The steering committee with the support of the scientific committee is working in these weeks to develop a program of initiatives to be implemented during 2023.”

“The Tower Oversight Group that I am honored to chair,” said Salvatore Settis, “is working with three fundamental points in mind. The first is the extraordinary feat and success of the Tower’s slope reduction techniques. The second is the impact that technologies, over time, even after the day the Tower was reopened to the public, have had on the monument. Technologies continue to develop, and it is necessary for this development to be reflected in a harmony between institutions: the Opera della Primaziale, a very old, very prestigious institution full of merit, has always followed and will always follow the monuments of the Square with the utmost care, and it also welcomes important synergies such as the one with the Ministry of Culture. Finally, the last point is the culture of preventive conservation, about which Giovanni Urbani, the great director of the Central Institute for Restoration, spoke at great length years ago, who put to good use the idea of planned conservation, of which the Tower of Pisa today is one of the greatest examples: not only has it been cured of a disease, the slope, by reducing it and bringing it back to the levels of 1810, but it is the subject of an extraordinarily sophisticated monitoring system that must, however, be continually updated and fine-tuned.”

“For being a patient with 850 years of age, an out-of-plumb of about 5 meters and a subsidence of more than three meters, the state of health of the Campanile is excellent,” Professor Viggiani explains. “To stay in the medical metaphor, everyone will remember that the patient had surgery 23 years ago; through a series of perforations (a kind of angioplasty) a small amount of soil was removed below the north side of the foundation, causing an imperceptible reduction in the slope. The monitoring of the steeple played an important role both in identifying the causes of the slope and in defining countermeasures to stabilize the monument. For this reason at the time of the dissolution of the international committee, on the instructions of the competent ministry, a monitoring group was appointed with the task of monitoring the evolution of the Tower’s movements and enfranchising the Opera della Primaziale in the delicate task of preserving the Tower.”

How is the Tower of Pisa? After 850 years, its condition is excellent

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