The bas-reliefs part of the column known as the Colonna Antonina located in Piazza Colonna in Rome have been recently restored so that even viewed from below it is possible to clearly distinguish the figurative elements. If one looks carefully between drums IX and X (of 17) a clear break will be seen cutting through soldiers, shields and steeds, which keeps the legs from matching with the bodies they belong to as though caused by some previous twisting along the contact surface – which is exactly what appears to have happened. In a period somewhere between the XIV and XVI centuries such structural damage might have been caused by a powerful earthquake – one of the hundreds of earthquakes past and present in the Mediterranean basin causing injury to persons and damage to the artistic and cultural heritage, the effects of which reach into places no one would have guessed.
Many today still believe that Rome is not subject to earthquakes, but this is a mere commonplace without basis: even the Eternal City has experienced – frequently enough – the movement of the earth below. In 1349 one or more earthquakes rocked the city, striking it at a time of pronounced weakness in the urban structure; inhabitants were few in number and ever-weaker monuments fell prey to the continuous plundering of metals and facing stone. For example, lead filling and iron framework were removed from columns and such. Rome actually suffers from three different types of earthquakes: those that occur in the Apennines (but also felt in Rome), which are the most powerful (such as the 1915 Avezzano earthquake, the last to strike a major urban area in Italy); those that follow one another linked to the late phase of volcanic activity in the Alban Hills in the Castelli Romani area; and those caused by a seismic charge all its own (located to the south in the Castel Romano area) that can reach up to VII on the Mercalli scale.
The dialogue among historians, archaeologists and engineers – which interdisciplinary discourse represents the true frontier in the environmental sciences – receives constant encouragement from the ample results obtained in the city of Rome, as well as from the innovative nature that characterizes research performed in environmental geography. In the period between 1968-1987 the overall expenditures by the Republic of Italy to redress damages caused by catastrophic natural events amounted to nearly 100,000 milliards of liras (in 1989 liras), a sum which could be decreased considerably with the realization of a decent programme of prevention. In the field of seismology such can come about only through a clear understanding of the past, and thus in constant interaction with historians and archaeologists. This is the crossroads where many current themes of scientific interest intersect, with the common denominator being mankind.
The socio-cultural dimension of seismic events has in any case attracted the attention of many humanists: “dragged” into this field the earthquake is viewed not as a scourge –as are floods or volcanoes – but as the event by definition, the palingenetic catastrophe, the sign of the divinity. It represents the overthrow of civilisation and the established powers; it is the Apocalypse striking rich and poor alike – or rather, in the past earthquakes struck the rich even harder than the poor because the rich had much more to lose living as they did in masonry palaces destined to suffer far more serious damage than the mud huts of others. Earthquakes accelerated processes of urban renewal and the reorganization of the territory, even if there was no lack of negative features to be deduced in the demiurgic characterization of the Architect. If anything, it remains to be asked why in modern times in contrast to the past earthquakes have become a tool for the consolidation of the powers that be and do not cause excessive upset (no more catastrofé, as the Ancient Greeks would have put it).
Concerted action by historians, archaeologists and geologists need not necessarily lead to the creation of a new field of study nor to a confusion of roles, but ought to at least allow the overcoming of problems related to the ongoing lack of a common language. Put bluntly, an historian ought to be expected to know about earthquakes, while an engineer ought not to reduce everything to columns of figures. At bottom this should be a voyage through space and time not limited to members of just any single discipline. After all, the questions raised are the same for everybody: Where? When? How great? What places show signs of ancient earthquakes, how great was the damage and what common features are present at different sites? A significant example of how archaeological, historical and geological data can be used to broaden and deepen knowledge about seismic risk in urban areas once again is provided by the city of Rome. There only 800 metres apart are found two monumental columns identical in terms of age, construction technique, and height – one dedicated to Marcus Aurelius, the other to Trajan. Only the former of the two has suffered serious earthquake damage, with dislocation in excess of a metre between drums IX and X, while only tiny breaks measuring just millimetres are found in the latter. Why? It all seems to depend on the geological makeup of the subsoil: while the bedrock of the city is made up of rather homogeneous Pliocene clays going hundreds of metres down, resting above are found types of terrain with different mechanical characteristics. The contrast between bedrock and surface covering (comprised of anthropic fill and alluvial deposits from the Tiber) causes an often considerable increase in seismic response. In addition, the presence of faults and fractures accentuates the contrasts in seismic response, putting d i ffering types of soils in contact with each other: What is found, then, is a systematic correlation between damage to structures and the geologico-structural position of the same, despite the fact that is not always a simple matter to establish a direct link with seismic events.
In the case of the Colonna Antonina the subsoil may have increased seismic waves in correspondence with the frequency characteristic of the monument itself, giving rise to phenomena of resonance.
An interdisciplinary approach of this type is new to the international scientific scene; it must act as a stimulus to the seismic classification of urban areas in relation to their geological characteristics and housing. Those buildings on mechanically poor land must be reinforced so as not to lose artistic or commercial value. The multidisciplinary nature of this type of studies does not appear to be detrimental to the specific individual skills of geologists, architects, engineers and historians, but rather is proof of the earth sciences’ social and decision-making role as distinguishing traits.