Conclusive remarks
Wherever in the world climate is mild, soils are fertile and seashore is nearby, humans have planned to settle down. This tendency has been emphasized in those settings where natural resources were easily available and/or ready to use, such as water, building materials, etc. These have certainly been among the primary conditions that favoured the urban growth through time in the Neapolitan district, despite the multiple sources of geohazards threatening the area: volcanic eruptions, bradiseism, earthquakes, landslides and cavity-related surface effects. The interaction among “positive” geoenvironmental factors and adverse driving forces increases with urban growth and therefore also the risk to human activity - depending on the particular geological and geomorphologic setting.
The evidence presented in this paper shows the strong correlation and conditioning of the local geology with the anthropic activities and the social and economic development of the territory. Excluding other human activity, such as agriculture, etc., which is also tied directly to the geology of the area, our attention was focused mainly on the “dependence” of architectural choices on the available territorial resources, as sharply observed by Rodolico: “…that a blindfold geologist entering a brand new town, unknown to him, will have information on local geology just by putting a glance on the materials used in the buildings”. All the available resources have been exploited by man since historical times. Most of them had a volcanic origin and, sometimes, were easily exploitable and workable, such as the tuff, thus becoming the fundamental element of the architecture of main and minor centres of the province. The good technical features of these rocks meant that they were in heavy use for structural purposes; outstanding examples occur in the several colonnades of cloisters of the ancient centre of Naples made up in Piperno. Obviously, whenever more precious materials were required for particular architectural elements, such as the portals of the numerous cathedrals and noble buildings, valuable imported materials were used (e.g., the Apuan Marbles).
Resources available in the territory were not only lithoid materials. Large quantities of incoherent materials such as pumices, sand and lapilli were exploited in several sites, mostly within the Campi Flegrei and from Vesuvian areas, subordinately, as raw materials for the production of cementitious mixtures. Although less important than the lithoid counterpart, these materials played a relevant role in the architectural heritage of Naples and surroundings. Pozzolana, in particular, because it made possible to obtain, much earlier than the discovery of Portland cement, hydraulic limes used to build important submerged works.
Undoubtedly the most frequently used material throughout the long history of the town and its province is the Neapolitan Yellow Tuff that has been in continuous use since Roman times. It must also be noted, however, that ignoring the well-known technical features and weaknesses of the tuff in some of the most recent urban works, anomalous (if not improper) uses have been recorded, as in the case of some external pavings that very rapidly underwent weathering phenomena, obviously because of their extremely low abrasive strength and/or the high content in pumice. A careful investigation based on laboratory tests, if not a mere bibliographical research, would have advised against the choice of a material notoriously unsuitable for such a purpose (de’ Gennaro, 2001). Since the 1990s, the use of NYT continuously decreased to the point of nearly complete stoppage, as has happened in the past for the other materials discussed in previous chapters. This decline was dictated by concerns about its exploitation - mainly with regard to environmental interest - rather than technical reasons.
On this account, one should not ignore the prospect of preserving these local stones, which were and still are so important in the history and the culture of Naples and, more generally, of the Campania region, by authorizing quarrying with modern and less invasive techniques, exclusively for restorations or for the construction of significant architectural structures. In this view, the Regional Plan of the Quarrying Activities (Regione Campania, 2006), comma 14 – Art. 89 of the Executive Rules (Norme di Attuazione) allows the quarrying of ornamental stone historical sites in protected areas (previously permitted by the competent authorities), on condition that the total area object of authorization does not exceed 1.0 Ha and 1,000 m3 of annual production.
It is a matter of fact that, in the last century, the Phlegrean-Neapolitan area underwent apparently uncontrolled development which compromised the environment and definitely increased the hydrogeological hazard. The abandonment by farmers of the most fragile areas enhanced this decay. Nonetheless, this territory still includes innumerable landscape and cultural resources which make it unique. It is foreseeable that future generations will be sufficiently wise to preserve this resource better than what was done by their ancestry.