Sometime in the fifth or sixth century A.D., a Roman consul named Decius Marius Venantius Basilius paid out of his own pocket to have the Colosseum repaired. Several columns in the stands that circled the arena at least 20 of them, maybe more had collapsed, crushing bleachers and balustrades. Sections of the underground chambers had been destroyed. Decius commemorated his contribution with an inscription on a stone that can still be seen not far from the monument's entrance. The damage, he wrote, had been caused by "the violence of a terrible earthquake."
The Italian capital isn't generally considered to be at high seismic risk but ever since I heard about the damage of the giant amphitheater, I've looked at Rome in a different light. The rest of the country is so often wracked by the trembling of the earth as evidenced by the recent destruction near Bologna. What kind of risks does the Eternal City face? The ground underneath is free of faults. Volcanic activity is mercifully distant. But the historic record tells a different story, of a city struck again and again by minor but nonetheless damaging earthquakes.
In 15 A.D., an earthquake collapsed a section of the Severan wall, according to Paolo Galli, a researcher at Italy's Department of Civil Protection, who has combed the historic and archaeological record for evidence of earthquake damage. In 801, another brought down the roof and rafters of St. Paul's Basilica. In 1044, the city trembled so hard church bells began ringing. The biggest event occurred in 1349, when, as recorded by the Italian poet Petrarch, "the ancient buildings neglected by the citizens and admired by the pilgrims fell down." The powerful earthquake battered the St. Peter's and St. Paul's Basilicas, took off the top of the Conti Tower, and likely destroyed the southern wall of the Colosseum. "Up until then, they were still using it as a bullring," says Galli. "From then on the Colosseum falls into neglect and becomes a quarry for travertine."
Galli is quick to downplay the risk faced by the city, pointing out that in Rome's more than 2,700-year history, it has seen only three recorded deaths from earthquakes all in 1812 when a house just outside St. Paul's Gate collapsed (many more have doubtless been unreported). The tremors that reach Rome usually originate some 50 miles or more away, in the geologically unstable Apennines. By the time the shock waves arrive, much of the energy has been dissipated. The shaking has never reached the intensities that destroyed much of the center of Aquila in 2009.
Yet, that doesn't mean that modern Rome is immune to the force of an earthquake. Damage from a temblor has two major contributors: the energy released in the tectonic slip and what's waiting to absorb the blow. Much of Rome is built alluvial deposits from the Tiber and its tributaries, stretches of loosely packed sand and clay that are not only susceptible to shifting during a quake. In the right conditions, they can magnify the power of a seismic wave. "A lot depends on where the houses are built," says Gian Paolo Cavinato, a geologist at the Institute of Environmental Geology and Geoengineering of Italy's National Research Council. It's no coincidence that it was the southern part of the Colosseum that suffered the most damage in 1359; the other half sits on a patch of firmer soil.
To make matters worse, much of the modern city was built during the post-war boom, when Rome spilled into what had until then been the surrounding countryside. In these neighborhoods, much was hastily built, with little attention to codes or permits. "The controls were a bit superficial," says Pietro Membri, president of Anaci, the National Association of Condominium Administrators. Later amnesties brought the buildings in line with the law of the land. But the laws of physics don't forgive so easily. The building I lived in until the end of last year, not far from the St. Paul's Basilica, is eight stories high, the last of which has been mandated to be left empty, for fear that occupying it would destabilize the construction. Across the street, another apartment complex has been torn down, after sinking soil caused it to start to lean dangerously. According to a 2011 survey by Anaci, one building in three in the city doesn't have an official certification of habitability.
What worries me most is how little attention is paid to the threat. The municipality hasn't set up any earthquake gathering points. Awareness in the schools is embryonic. In offices, it's non-existent. There's no discussion about bringing Rome's housing stock or workplaces up to modern earthquake codes. The analogy that keeps springing to my mind is of a storm that swept through the city this winter. It wasn't much of a snowfall by the standards of many other cities no more than six to eight inches but it caught its residents completely unprepared. Taxis without snow chains fishtailed in the streets. Traffic on the ring road came to a complete halt. The schools and public building were closed for days. Nobody had planned for it because nobody expected it to happen.