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GSA TODAY | MAY 2015 construction and, at the peak of Rome’s development,
>80,500 km of roads were stone-paved. The Romans also had a
large availability of sands, clays, and gravels deposited over time B.C. 414 and B.C. 4 (Bersani and Bencivenga, 2001), although the
by the Tiber River (Heiken et al., 2007). The abundance of these
materials promoted the manufacture and use of bricks, which
became very common in Roman buildings. Like Rome, Naples
was built on volcanic hills, with the eastern remnants of several
coalescent tuff cones and lava domes forming the Phlaegrean
Fields (Fig. 1), which were emplaced prior to the violent erup-
tions of the Campanian Ignimbrite (39 ka) and Neapolitan
Yellow Tuff ignimbrites (NYT; 15 ka). The unconsolidated facies
of the NYT (pozzolana) were also frequently used to produce
hydraulic cements. The NYT represented a solid but soft and
easily workable ground layer for buildings, and for digging
cisterns and sewers. It was the most widely used building stone
in Neapolitan and regional architecture since Greek times
(Cardone, 1990; de Gennaro et al., 2000). The urban develop-
ment of Naples was strongly determined by the underground
exploitation of tuffs that created a network of caves and tunnels
(Cardone, 1990). Building materials were one of the most
important economic resources for both Rome and Naples, and
so mining became a very significant industry.
Both Rome and Naples suffered risks associated with frequent
earthquakes, flooding, and CO2 and radon emissions. Seismicity
in Rome and Naples was, and still is, mainly associated with two
distinct seismogenic areas; namely, the Apennines and the
volcanic districts. Earthquakes of VII–VIII Mercalli-Cancani-
Sieberg scale (MCS) maximum intensity have occurred in Rome
and Naples and were the result of the present extensional regime
related to post-orogenic collapse of the Apennines (D’Agostino
et al., 2011). The greatest effects of these earthquakes are felt
where there is an alternation of soft, loose alluvial and coastal
sediments with the more rigid bedrock (marine clay and
volcanic sediments). The alternating soft and rigid sediments
give rise to an anomalous amplification of ground motion
causing buildings to be subjected to long and strong shaking;
this occurred in both the historical center of Naples (Nunziata et
al., 2000) and along the Tiber river valley in Rome (Heiken et al., prompted the urbanization of areas subject to natural hazards,
2007). In addition, the low-lying geological setting of Naples has
been affected by huge natural and artificial geomorphological
changes (Nunziata et al., 2000). Volcanic earthquakes, with
maximum intensity of VIII MCS, have originated in the volcanic
areas of the Alban Hills since Roman times, while eruptions of
Vesuvius have often been accompanied by large earthquakes in
the Apennines, 50–60 km to the northeast, such as those that
occurred in 63 A.D. and 64 A.D., before the destructive Vesuvius
eruption in 79 A.D. The Neapolitan area is also affected by
bradyseism, the subsidence and uplifting of the ground surface
caused by the volcanic and hydrothermal systems beneath the
Phlegrean Fields.
Both Rome and Naples developed during long quiescent periods
of their volcanoes. The last known eruption of the Alban Hills is
dated ca. 29,000 yr B.P., although more recent phenomena of lahar
generation from the crater of Albano have been identified
(Funiciello et al., 2003). Similarly, the ancient development of
Naples mainly took place during the 3,000 years of quiescence of
the Phlegraean Fields and Vesuvius before the 79 A.D. eruption.
Flooding also represented another important hazard both in
Rome and Naples. Because of its location close to the Tiber River
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delta and on parts of its alluvial plane, Rome has frequently been
afflicted by floods. Fifteen floods have been described between
Tiber was generally considered as a calm river with few floods. Up
until Republican Times, flood damage had not been devastating
because competent city planners had placed facilities on the flood-
plain and most residences on hilltop areas. However, during the
Imperial period (B.C. 27–395 A.D.), settlement was also allowed
across the floodplain up to the Tiber’s banks, as a result of which a
large proportion of the city’s population was exposed to flooding
(Lamb, 1995).
On the other hand, flooding has been a regular phenomenon
throughout the history of Naples. The city developed in an area
where torrential rain-fed waters flowed into several rugged
canyons or gullies on the mountains that unified at the back of
the city. The first flood records of the city date back to 1010 A.D.,
but thick alluvial deposits in the central area of the city testify to
the occurrence of floods in pre-Roman time.
Magmatic activity and fault systems are also responsible for
elevated toxic gas concentrations in the near-surface environ-
ments of Naples and Rome, with the gases produced at depth
migrating upward along highly permeable fault zones. The most
common gases are CO2 and H2S, likely formed by magma cooling
and degassing, and by water-rock interactions. Sudden releases of
CO2 have been documented from antiquity until the present day
in several areas of the Alban Hills volcanic district. The quantity
of CO2 that rises from the depths and subsequently dissolves into
shallow groundwater has been estimated to be more than 4.2 × 109
mol year −1. In addition, elevated Rn comes from the high content
of U and Ra present in both volcanic lavas and tuffs. In the
Phlegraean Fields volcanic area, many hydrothermal phenomena,
such as fumaroles and hot springs, testify to the still active volca-
nism of this area.
Finally, both Rome and Naples have been affected by anthropo-
genic hazards. The fast growth of the cities and their populations
such as river and coastal flood plains previously used for agricul-
ture, thereby exposing the population to flood risk and also
reducing the ability of the city to ensure self-sustenance. Another
hazard affecting both cities stems from the underground cavities
that remained after the prolific quarrying for building materials.
The subterranean tunnel networks were so dense and intricate
that the vaults of the galleries were prone to collapse. In addition,
the lack of a clear separation between water cisterns and sewers
exposed the population of Naples to diseases such as cholera.
During late Republican time, continuous construction of new
buildings, higher consumption of goods, and the generation and
burial of the resultant waste increased the rate at which both cities
rose above their original geologic foundations. In the Tiber flood
plain of Rome, the anthropic debris layers are 10–15 m thick. In
the historical part of Naples, the same deposits can locally reach
thicknesses of 20 m (Nunziata and Panza, 2002). Debris layers
generally have very poor geotechnical properties and so provide
weak foundations that, in the event of an earthquake, can actually
magnify seismic waves.
Urbanization also caused degradation of the hill slopes,
creating unstable geomorphological conditions that can trigger
landslides, especially during the occurrence of seismic tremors.
The earliest evidence of slope instability and mass movement in