An Investigation into the Enigma of the 1823 Fire at St Paul Basilica in Rome

In commemoration of the two hundredth anniversary of the fire that on 16th July 1823 destroyed a wide part of the Basilica of Saint Paul Outside the Walls in Rome, several texts have analysed the political and cultural context of the time, as well as various aspects of the reconstruction of what was, before the fire, the basilica most visited by pilgrims in Rome. The basilica damaged by the fire of 1823 had been built under the reign of the emperors Theodosius I, Gratian and Valentinian II around the end of the fourth century, in the place where tradition placed the burial of the apostle Paul and where the emperor Constantine had built a smaller basilica. Among the different characteristics of the building, construction and location aspects of interest for the investigation will be described.

A vast historical literature tells the story of the basilica up to the fire and the subsequent reconstruction. In contrast, there have been no published texts that explore the cause of the fire according to a rigorous investigative approach. Recognizing this gap, the 2023 paper “The Fire of Saint Paul Outside the Walls: a very retrospective scientific investigation“, drawing on contemporary sources, aims to highlight some inconsistencies in the official accounts, presenting the cause of the fire more as an enigma to be solved than as an established fact.

Method of the investigation

Thus, the authors undertook an exploration according to the scientific investigation methods outlined in the National Fire Protection Association standard NFPA 921-2021 “Guide for Fire and Explosion Investigations”.

As for the sources, newspaper accounts from the time of the fire attributed its cause from the very first hours to the negligence of workers charged with repairing the roof or, according to some accounts, the gutters. A few days after the fire, the Diario di Roma also saw fit to publish an account of a fire on the roof of the Basilica of St. John Lateran due to the carelessness of the workers. The account written by the monks of the Monastery attached to the Basilica went into great detail, linking the event to a dispute between bricklayers and tinsmiths.

Uncertainties

However, critical details remain elusive in all the accounts: no one saw fit to explain what construction equipment was in use on the roof on the evening of the fire. Much less was the nature of the work in progress clearly clarified, and how burning coals could have fallen onto the wooden elements without the workers noticing. Finally, the total secrecy about the names of those responsible, released after little more than a day in prison, cannot be explained by such a serious crime.

In response to these uncertainties, the authors have tried to clarify the origins of the fire by juxtaposing historical sources with recent research results on the mechanisms of ignition and propagation of wood combustion.

The historical information presented in the document is based primarily on chronicles published between July 16 and 31, 1823, with additional references to various manuscript documents associated with them. In particular, details regarding the basilica and its condition were extracted from the writings of Nicola Maria Nicolai and Angelo Uggeri.

The Diario di Roma, a journal covering local and international issues, played a crucial role in providing insights into the state of the basilica and the damage inflicted by the fire. Issues dated July 16, 1823, and July 26, 1823, addressed these aspects. The magnitude of the damages becomes apparent through a multitude of images created by painters and engravers in the weeks immediately following the incident. These artists were drawn to the significance of the building and the gravity of the event, reflected in their works.

In unraveling the mysteries surrounding the 1823 fire at St. Paul Outside the Walls, the absence of direct testimonies from involved workers and the lack of information on the ongoing work make it challenging to definitively identify the ignition and propagation mechanisms.

Smouldering combustion is not the only hypothesis

To introduce hypotheses on the causes of fires in the field, the authors state that: “In the immediate aftermath of the fire, all the chronicles agree on the fact that maintenance work was underway on the roof, which was the only combustible structure of the building. Therefore, following the information provided by the chronicles, the main and secondary wooden framework of the roof is the construction element from which the authors have investigated the dynamics of the early stages of the fire. In general, the main causes of accidental ignition in a building where, like the basilica of 1823, there are were no systems fueled by electricity or by flammable or combustible materials, can be traced back to lightning or to the improper use of open flame lighting devices (torches, lamps, candles). No documents of the time report meteorological perturbations, while according to the anonymous “Postilla”, three people would have gone to the roof structure to carry out some surveys, an activity that after sunset would have needed the use of torches.”

Therefore, the authors state that the analysis of the documents leads to two plausible scenarios. The first, which constitutes the only cause considered historically, is an accidental event with the fall of burning coals during construction work, which led to slow combustion. The second, which appears at least equally plausible, is a fire started after the end of the day’s work. The ignition in this case could have been accidental or intentional.

The lack of testimonies given by the directly involved workers and of information on the type of work in progress and on the extent of the fire at the time the fire was seen, prevent from corroborating both hypotheses.

According the authors, “The widely accepted theory of smouldering combustion faces challenges in explaining the delay between ember fall and the manifestation of flames, especially considering the timeframe from site abandonment to fire detection. Additionally, an alternative scenario proposed by the “Postilla anonima” suggests intentional acts after workers left the site, supported by the absence of workers’ names in chronicles and ongoing investigations weeks after the incident“..

Considerations on the sidelines of the study

An interesting issue to outline the climate of the time has not been addressed by the authors of the publication. It concerns the 20 July 1823 fire of the Church of the Espíritu Santo in Madrid (Spain), which was most likely carried out to assassinate the Duke of Anguleme, commander of the French troops intervening in Spain. The act was probably the work of political opponents of the return of the French forces and the absolutism of Ferdinand VII, and was part of a very violent period in Spanish history, where the conflict between monarchists and liberals had reached its peak.

Although no victims were recorded on that occasion, the fire was started with many people present in the building, who were therefore exposed to extremely serious danger. In this regard, the soldiers who saved the Duke were awarded commemorative medals.

The peculiarity of the date on which the fire in Madrid occurred, four days after the fire at St. Paul’s in Rome, could have led the Roman authorities responsible for security to suspect a plan to destroy Catholic places of worship. This reason could justify the fact that, shortly after the fire, very severe measures were adopted to protect St. Peter’s Basilica and other churches in Rome.

More on the context of St. Paul fire

• Professor Richard Wittman’s upcoming book “Rebuilding St. Paul’s Outside the Walls – Architecture and the Catholic Revival in the 19th Century” scheduled for release in 2024
• Nicola Camerlenghi’s St. Paul’s Outside the Walls – A Roman Basilica, from Antiquity to the Modern Era.
• Reconstruction of the St Paul outside the Walls Basilica