Not only the skilled hands of master architects, who over the centuries have shaped the present-day magnificence of the city of Rome in marble and tuff. The Urbe, in its more remote past, was designed also by another unattainable artist, nature in its most violent and irrepressible form.
In late antiquity and the early Middle Ages, in fact, over a long period between the XNUMXth and XNUMXth centuries AD, the city was hit by some seismic events that contributed to significantly modifying its profile, leaving traces that can be found still today, reconstructing, piece by piece, a natural history that inevitably merged with the archaeological one and with the countless vicissitudes of the men and women who inhabited the seven hills before us.
Thanks to geoarchaeology and, more precisely, to archeoseismology it is in fact possible, even after almost 2000 years, to give a new reading to what emerges from archaeological excavations, which are no longer "only" the historical-artistic heritage of the nation, but they also become a very precious testimony of the geological history of our country, revealing the relationships between the history of our ancient fellow citizens and the stresses coming from the surrounding environment and nature.
We have tried to orient ourselves in this maze of evidence of the seismic past which, over time, has redesigned the city of Rome, letting us be guided by Fabrizio Galadini, research manager of INGV, who has been engaged for years in the study of various archaeological sites in order to reconstruct the seismic history of our country.
Fabrizio, what do we mean when we talk about archaeoseismology?
Archaeoseismology is the discipline that deals with identifying the traces of past earthquakes in archaeological stratigraphies. These traces obviously date back to a pre-instrumental age, i.e. they refer to seismic events prior to the appearance of instruments used to record earthquakes. They concern buildings or artifacts discovered with archaeological excavations, preferably recent, and therefore built with a stratigraphic method, or present always in the monumental context of a city (think, for example, of the Colosseum, which has been imposing itself on the view of citizens and visitors for millennia).
How is an archaeoseismological investigation carried out?
The data acquired during an archaeological excavation, for example those relating to wall remains found in a collapsed position, are integrated with information from geological, geomorphological, geophysical investigations, as well as, naturally, with knowledge of historical seismology, if available. The picture thus defined, in order to quantitatively clarify its compatibility with the effects of seismic shaking, can be compared with the results of engineering modelling, for example those which simulate the response to the dynamic stresses of ancient buildings for which reconstructive hypotheses are available.
The information deriving from these investigations allow, on the one hand, to broaden the knowledge on the seismicity of the past (fundamental for seismology in consideration of the rarefaction of written sources, which unfortunately give us little information on events more than a thousand years ago), from 'other are also of interest to those who, like the archaeologist, need to reconstruct the history of an ancient site, enriching the framework of knowledge with the introduction of any "interference" of natural events (such as an earthquake ) which, by damaging the site itself, have affected its continuity of life.
How can these reconstructions contribute to our daily activities?
Well, undoubtedly reconstructing the history of the sites in relation to the manifestations of the natural environment which, historically, have produced damage to certain archaeological sites is fundamental, for example, to set up a work of prevention: the natural criticalities and territorial fragilities which have "conditioned" an area in the past could, in all probability, also recur in the future.
Let's talk specifically about Rome. It is known that in late antiquity and in the early Middle Ages the city was affected by several earthquakes of considerable magnitude: according to the knowledge we have today, what impact did these seismic events have on ancient Rome?
Thanks to archeology and written sources we have various images of Rome between late advanced antiquity and the early Middle Ages. Over time, the degradation of the monumental appearance typical of the early years of the empire becomes clear. The testimonies tell us of a city that, over the course of a few centuries, has undergone a strong demographic contraction and the consequent reduction of inhabited spaces, a crisis that would seem very evident especially starting from the so-called Gothic War, in the first half of the sixth century (it was fought between 535 and 553 and saw the Byzantine Empire oppose the Ostrogoths).
In this context of abandonment, we wondered if the earthquakes between the XNUMXth and XNUMXth centuries - including some that we know from written sources had exceeded the damage threshold - could have played a role in this transformation of the city, and the answer was positive .
What were these strong earthquakes?
Those known from written sources, which affected Rome between the 443th and 484th centuries, took place in 508, close to 618 (or 801, the epigraphic source does not allow us to determine the date of this event unequivocally), in 847, in 618 and in XNUMX. For the latter, as for the earthquake of XNUMX, the sources do not mention damage to the city – damage which however may not have been mentioned and which therefore cannot be excluded. In fact, the archaeological sources in turn clarify that these earthquakes probably contributed to the creation of a sort of ruined landscape in what today is the historic monumental area of Rome.
In addition, clearly, to the extent of the seismic events, to what was it possible to attribute the cause of their strong impact on the city?
Among the main reasons for the significant damage that emerge from the archaeological investigations, it is conceivable, on the one hand, the age of the buildings (which, between the XNUMXth and XNUMXth centuries, began to have, in many cases, several centuries of life), on the other stripping works of parts of the buildings, sometimes with load-bearing function, which were used elsewhere to build new structures.
Where were the major damages of the earthquakes of the past located in the Rome that we live and know o
today?
In reality, on the basis of the information we have available today, we are not able to define a zoning of the damage, since it is knowledge resulting from analyzes that arise with archaeological excavations, therefore acquired punctually and with a very discontinuous. Archaeological intervention is often the result of investigations prior to the creation of modern artefacts. Think of the large amount of scientific data that are produced with the excavations for the construction of line C of the Rome underground.
In this sense, therefore, we cannot have a 360-degree view of the distribution of collapse units attributable and compatible with seismic events in the central area of Rome. However, in the case of more recent earthquakes, of the modern and contemporary age, the research conducted a few decades ago by colleagues from various institutions had already defined a distribution of damage that also depends on the geological characteristics of the foundation soils. The damage in many cases seems to be concentrated in the alluvial areas. These are the so-called "site effects", an area of investigation that would require a separate study involving other colleagues from INGV. Simplifying a lot, it can be remembered that the sediments of fluvial depositional environments can lead to the amplification of the seismic motion, the consequences of which often translate into an increase in damage.
The symbol par excellence of Rome in the world is, as we know, the Colosseum. Have you ever suffered earthquake damage?
Absolutely yes. A first possible reference is 443: however, it is a complex reconstruction. Indeed, although it is an earthquake documented by the sources, and in particular by Fasti Vindobonenses Posteriors, in this case there are no explicit references to damage to the Colosseum, although traditionally it is believed that the amphitheater suffered the effects of the earthquake. On the other hand, there is an epigraphic testimony that testifies to the reconstructions of the Colosseum cared for by Praefectus Urbis Rufius Caecina Felix Lampadius, chronologically compatible with that earthquake. However, the cause of the interventions (that is, whether they are a consequence of the seismic damage) is not mentioned. Also in another epigraphic fragment reference is made to restorations and the seismic cause, through the integration of the text, has been hypothesized by those who have studied the still legible part.
There are instead no doubts about the damage caused to the Colosseum by the earthquake of 484 or 508: in fact, in the epigraphs that testify to the interventions “arena and podium” the seismic cause is explicitly mentioned (“abominandi terraemotus"). This earthquake probably originated in the Apennines, triggered by the Fucino fault, which in 1915 seriously damaged many towns in central Italy.
After that, coming to a decidedly more recent past, there are numerous other traces that indicate further damage suffered by the Colosseum, such as those of the earthquake of 1349, the effects of which in Rome were described, among others, also by Francesco Petrarca.
We can therefore undoubtedly say that the Colosseum has a rather long seismic history, and what we see today is certainly, in part, the result of this past.
How might today's Rome react to an earthquake of similar proportions to those of late antiquity?
First of all, we must consider that today's Rome is quite another thing than the one built inside the walls of the imperial era. With the unification of Italy, the role of capital led to the progressive and rapid increase in population with the consequences of the expansion of the built-up area. The urbanization of alluvial areas brings us back to the aforementioned problem of site effects, to which is added the vulnerability of buildings which, considering the building expansion phase of the first half of the last century, are starting to be a hundred or more years old since their construction. All this clarifies the difficulty of defining in a few words what could happen in Rome, today, in the event of a strong earthquake, for example like the one of 1915 (stronger than those of 2016 and moreover with an epicentral area closer to the capital) .
Will INGV continue to collaborate in archaeoseismological investigations?
Absolutely yes, both in Rome and outside. The collaboration with officials of the Special Superintendence of Archeology, Fine Arts and Landscape of Rome began several years ago and the investigations in the archaeological excavations are repeated every time something potentially attributable to the effects of earthquakes emerges: the last intervention, which began about a year and half ago, we did it on a large excavation carried out for the construction of a system pertaining to Metro C in the area of via dell'Amba Aradam, near Porta Metronia. Even there, for example, the compatibility with the sudden collapse attributable to a seismic event was estimated for the collapsing position of the remains of a large building.
Then there are the collaborations with the officials of the other Superintendencies, that of Abruzzo, those of the Lazio territories, some recent activities carried out in collaboration with the Archaeological Heritage Office of the Province of Trento and so on. The Institute is therefore fully engaged in terms of interaction with the institutions responsible for the protection and conservation of cultural heritage.