Deciphering the effects of human activity on urban areas through morphostratigraphic analysis: the case of Pisa, Northwest Italy

Type, thickness and volume of anthropogenic deposits, buried beneath long-settled cities, are good indicators of the human impact on urban environments and topography. Pisa is multilayered city settled since Etruscan times in the lower Arno Plain. Stratigraphic and geomorphological data from the urban subsurface show that Pisa today is located on a mound (ca. 4 m-high) made up dominantly of anthropogenic deposits. Two types of anthropogenic facies are distinguished: human-modified deposits of Etruscan Age and made-ground deposits dated since the Roman Age onwards. Integrating subsurface stratigraphy with ancient ground levels topography, we reconstruct the evolutionary phases of Pisa urban landscape subject to a dominant human influence. Urbanization processes started at Etruscan times, as testified by the lower boundary of the anthropogenic succession (Pisa archaeosphere). The formation and the highest increase in elevation of Pisa mound, that is still growing, occurred during the Roman and the Middle Ages. At the same time the urban fabric moved southward, toward the Arno river, and a thick anthropogenic succession accumulated in the city sector where ancient ring of walls had been hypothesized. However the highest acceleration in the urban ground growth rate is recorded since 1950 AD onwards, corresponding to the Anthropocene “Great Acceleration”.