Geological-geomorphological conditioning on the development of historical centers: the example of Gubbio (Umbria, central Italy)

Gubbio (Umbria, central Italy) was built on the slope of Mt. Ingino (908 m asl), on the left bank of Torrente Camignano, where the vast flat area known as the “Gubbio Plain” begins. The debris at the base of the slope of Mt. Ingino is delimited by two alluvial fans, one of the Torrente Camignano at NW (almost flat) and the other of the Fosso Cavarello at SE (more steep). The slope debris shows an evident morphological step (H max. about 20 meters) oriented parallel to the slope itself. This produces a marked discontinuity in the slope profile and affects the whole width of the detrital body. This kind of escarpments is frequent on the slope debris at the base of the mountains of the Gubbio chain. This ridge constitutes the NE flank of an anticline, formed during the Apennine orogeny. It is broken at the core by a normal fault with considerable upthrow (over 1500 meters) and with direction parallel to the axis of the fold itself. These escarpments are likely to be interpreted as the surface morphological expression of recent phases of tectonic activity linked to the Gubbio fault (which, therefore, has to be considered an active and capable fault). A bull of Pope Clement III in 20 October 1188 and a diploma of Emperor Henry VI in 5 June 1191 suggest that when the Eugubini (the people of Gubbio), in the second half of the 12th century, decided to build the new city “on the mountain”, they identified how the most suitable place for the fortified urban space, the one upstream of the great escarpment which divided in two parts the slope debris of Mt. Ingino. Later, especially during the 13th century, a consistent urbanization took place in Gubbio. This led to an inevitable expansion downstream of the urban core, which essentially took the shape of the current historic center of the city. On the specific topic of the relationship between the definition and development of the late medieval city of Gubbio and the conformation of the slope debris on which it was built, some preliminary considerations have already been formulated (Sannipoli, 2013). The research in progress is aimed at investigating some specific aspects of this interesting problem of urban geomorphology, both as regards a more precise definition of the geomorphological characteristics of the site, and in relation to the transformations of the first urban core of Gubbio, over the 13th and 14th centuries. Above all, it seems interesting to define what these transformations entailed, as regards the alterations of the geomorphological peculiarities of the site where the city was born and had subsequently developed.