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Figure 1. Main geological characteristics of south-central Italy, where the cities of Rome and Naples are located (modified from Butler et al., 2004).
to live, with far fewer incidences of marsh fever, which largely
affected the alluvial areas. The hills were created by the fluvial
erosion of an ignimbrite plateau sloping gently from the Alban
Hills volcano to the southeast. Because of this geomorphology,
and the presence of the Monte Mario–Gianicolo ridge to the
northwest, Rome naturally expanded to the southeast. The topog-
raphy in this direction provided an area of ~800 km2 for the
expansion of the city and agriculture and also provided an easy
route along which to construct aqueducts.
Naples, on the other hand, was located within an easily defend-
able bay that drove an economy dominated by sea trade. But the
rugged geomorphology of its interior territory significantly
limited any other potential of the city. The Vesuvius and
Phlegrean Field volcanoes defended the city from possible
invaders, but they physically blocked any inland city expansion
and made communication and trade with the hinterland popula-
tion difficult. Over time, Naples mostly grew vertically, using as
foundations the natural marine terraces bordering the coast.
Geomorphology therefore played an important role in the deci-
sion of the city to develop an economy centered on the marine
trade rather than agriculture.
An economy based on agriculture was much better suited to
Rome, which had an abundance of fertile soils derived from
volcanic and alluvial sediments. Farms were plentiful, even
inside the city walls, and were mostly on the alluvial plains; they vated at increasingly longer distances from building sites (de Rita
were small and family owned and ensured the self-sustenance of
the city.
Rome was also favored by an abundance of water resources,
such as the Tiber and Aniene rivers, and several natural springs
present inside the city walls. Before the construction of the first
aqueduct, the Aqua Claudia (B.C. 312; 400 years after the birth of
Rome), at least 23 natural springs, with an average flow rate of GSA TODAY | www.geosociety.org/gsatoday
more than 80 L/s, provided Rome with water. In addition,
Romans drank water from the Tiber and Aniene rivers. These
rivers were also highly navigable and so represented an easy and
direct route for communication and trade with the hinterland.
Conversely, the city of Naples did not have large freshwater
resources and lacked natural springs. It also had no river and so
lacked this convenient means of delivering goods to the hinter-
land. Most of the water in Naples was collected from shallow aqui-
fers through a system of wells or water tanks, with a total surface
area of ~10,000 m2, that stored rainwater (Kosso and Scott, 2009;
Montuono, 2010). The first aqueduct, the Serino, was built during
the age of Augustus (B.C. 27–14 A.D.). However, it subsequently
suffered damage from the earthquakes that preceded and coin-
cided with the Vesuvius eruption of 79 A.D.
The geological settings of Rome and Naples provided solid
foundations and large resources of several different types of
construction material. The ground layers for foundations both in
Rome and Naples were mostly made of tuffs and consolidated
coastal or alluvial sediments. Rome’s foundations are mostly on
pyroclastic deposits from the Sabatini and the Alban Hills
volcanic districts (Fig. 1). Both volcanoes emplaced several large-
volume ignimbrites, mostly comprising lithified tuffs that were
often used as building stones. Over time, rocks with increasingly
better physical-mechanical characteristics were chosen and exca-
and Giampaolo, 2006). In the late Roman Republic, the use of
pozzolana (loose scoria ignimbrites) to make concrete was intro-
duced. By mixing pozzolana with lime, Romans created a
hydraulic cement that improved their ability to construct infra-
structure, even underwater. Rock lavas were used for road
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