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Figure 2. Evolution of Rome from Archaic to Imperial times (Häuber, 2014).
Naples has been discovered in its ancient center, where the city covered by construction and consequently the agricultural areas GSA TODAY | www.geosociety.org/gsatoday
market of the Imperial period (first century A.D.) is partially within the walls disappeared. From revenues of ~540 million
buried under a chaotic deposit dated to the end of the fifth sesterces, state expenses included 108 million sesterces to import
century (Di Martire et al., 2012). Landslides in and around the 3.5 × 105 tons per year of wheat to sustain as much as half the
Neapolitan area have mostly been related to human activities population. In addition, 31–65 million denari (1/4 denario =
(around 40%), such as trenching, excavations, and quarrying 1 sesterce) was devoted to military operating costs. Kehoe (1988)
(Calcaterra and Guarino, 1999). Hill slope instability in Rome estimated that, during the Roman Empire, the population
was limited and mainly human-induced when urbanization consumed ~200,000 metric tons of wheat annually. A family of six
expanded to the margins of valleys. people needed to grow crops on at least 3 ha of land in order to
survive. This meant that for self-sustenance, the Roman popula-
DISCUSSION AND CONCLUSIONS tion needed at least 500,000 ha, an area of land greatly exceeding
that which was available around Rome. So Rome became depen-
Geology was a major contributor to the fortune of Rome, which dent on food imported from overseas to feed the general popula-
had more resources and reduced risks relative to Naples. Rome tion and had to harness the resources of its provinces in order to
could also safely expand toward the Alban Hills area because of feed and support the revenue of its army, which was spread
the plateau geomorphology, which further provided an easy path throughout the empire.
for the construction of the aqueducts. The city could also develop
agricultural practices that, until Republican times, ensured its Naples had a different set of problems due to its geological
self-sustenance. setting and interactions between natural and anthropic dynamics
that culminated in numerous risks. Primarily, the difficult terrain
Many lessons can be learned if we consider the development of surrounding the city severely limited urban expansion (Fig. 3).
Rome over time (Fig. 2). Rome evolved from a small village that Steep hills and narrow, abrupt volcanic ridges formed unsur-
covered just over 100 ha and was enclosed by a perimeter wall of mountable obstacles not only to city expansion but also to
7 km. During Republican times, it expanded and was enclosed by communications with the hinterland. This rugged geomor-
the 11-km Servian wall. During Imperial times, Rome doubled its phology and bradyseism forced the city to grow vertically, with a
size in less than 300 years, attaining a perimeter of 19 km enclosed resulting increase in landslide risk. To add to Naples’ problems,
by the Aurelianic walls (Häuber, 2013). During this time, the water resources were scarce and flash-flooding resulting from the
population increased to > 1,500,000. The alluvial areas were fully
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