Pisa and Its Natural Environment

A series of palaeogeographic scenarios related to the last six/seven thousand years can be reconstructed on the basis of a multidisciplinary investigation integrating the geomorphological, stratigraphic, and palaeontological data of the first ten-to-fifteen metres of the sedimentary succession buried beneath the urban and suburban areas of Pisa. Such data indicate that: 1) the vertical succession of facies associations (lagoon, paludal areas, poorly drained and drained floodplain) demonstrates a progressive emersion of the study area starting from about 5000 cal, according to the general deceleration of the sea-level rise and to the end of the climate optimum accompanied by drier conditions; 2) from the Eneolitic period to Modern Times, the Pisa plain has been crossed by a complex hydrographic network composed of branches belonging to both the Arno and the Auser (the southern branch of the palaeo-Serchio) rivers. The frequent changes in the course of both rivers actively contributed to the development of the plain. The Auser in particular remained the principal river of the city until the Roman period when the focus started to shift to the Arno; 3) during the proto-historic and Etruscan period the hydrographic networks determined the development of backswamps within the Pisa urban area, where the earliest traces of a continuous settlement were found; 4) a well-drained plain developed during the Roman period, while wetlands developed outside the city walls in the Middle Ages. Their origin and possible relationship with a phase of contraction in the urban fabric remain undetermined; 5) humans adapted to a constantly changing natural environment instead of making substantial modifications. This adaptive approach is demonstrated by the direction of the principal roads, the location of port facilities, and the choice of a naturally elevated area for city development; 6) human modification to the environment started in the Roman period and included improved drainage of the plain achieved by centuriation, subsequent development of a drained floodplain, and an increase in the rate of soil aggradation in the urban area. The Pisa plain thus provided humans inhabiting this area with advantages and challenges that defined their interaction with the natural environment. The development of the urban center and its countryside was shaped by this interaction, which over millennia have been in a constant state of redefinition. Both hydrographic network and palaeomorphology have clearly influenced the development of the city’s plan since its inception (eighth century BC), favouring a concentration of buildings on the reliefs near the Auser and later along the Arno. The path of the main Roman arteries of communication, the Via Aemilia Scauri and the Via Aurelia, were also influenced by the surrounding morphology, with the former being more or less parallel to the existing course of the Arno river, while the latter followed the beach ridges of the developing Arno delta system. The delicate balance of human intervention and natural transformation of the landscape formed the foundation for the creation and development of ancient and medieval Pisa, confirming the close interconnection between history, geography, and geomorphology.