LA CITTÀ DI FORUM SEMPRONII E I SUOI RAPPORTI CON IL PAESAGGIO ATTUALE: UNA DISCUSSIONE BASATA SU EVIDENZE GEOLOGICO-GEOMORFOLOGICHE E ARCHEOLOGICHE

Abstract

Savelli D., Luni M. & Mei O., The town of Forum Sempronii and its relations with the contemporary landscape: a discussion based on geologic, geomorphologic and archaeological evidence. (IT ISSN 0394-3356, 2004).
The Roman town of Forum Sempronii, founded between 132 and 126 b.C., is set near the modern village of San Martino del Piano, ca.
2 km to the east of Fossombrone. The ancient settlement rests on the flat surface of a wide upper-Pleistocene terrace of the Metauro
River, ca. 20 m above the modern stream. At least three sides of the Roman town walls took advantage of geomorphologic elements.
Indeed, they were against the foothill to the north; to the west they ran along the edge of a steep scarp on the left of Fosso della
Conserva (a small left-tributary stream of the Metauro River), and they rose southwards on the edge of the Pleistocene terrace. The
eastern side is more problematic as regards both its true position and its relation to some specific landform: in all probability it developed along the bank of a no longer recognisable gully. One of the most important features of the modern landscape in the vicinity of the archaeologic site is a roughly flat-bottomed, broad semicircular depression representing a pronounced relict meander of the Metauro River. It is entrenched into the upper Pleistocene terrace unit and bounded to the north by the terrace scarp on which the southern wall of the Roman town was built. Hence, the scarp enclosing the abandoned meander separates the upper-Pleistocene terrace alluvium from the Holocene one: it is well-preserved, with a sharp upper edge and scarce colluvium/debris accumulation at the toe.
Furthermore, the abandoned Metauro River channel is still well recognisable along almost all the scarp toe. The excellent preservation
of such landforms hints at quite a recent cut-off of the meander neck and abandonment of the previous course. Moreover, the very
occurrence of rounded Roman bricks and tiles in alluvial deposits at the mouth of the abandoned meander hints at a recent fluvial activity on at least a sector of the relict fluvial bend. Finally, maps dating back to 16th –18th century show that the meander at issue was already inactive and only minor adjustments of the fluvial course did occur at its mouth. On the basis of these considerations, and
since important modifications of fluvial-channel patterns in nearby areas can be ascribed to late Roman-early Medieval times, we can
speculate that the “roman” Metauro River flowed through the abandoned meander of today, close to the southern walls of the town.
The presence of a large fluvial channel just close to the town walls would have enhanced their defensive effectiveness. Indeed, its vicinity to the river would have made the southern side of the town the more defensible one as well as a preferential way for watering.
Moreover, the presence of an active channel at the foot of the scarp would have been able both to improve gully development and to
sustain existing gullies free from debris-filling, thus allowing ditches similar to the one which has been hypothesized to border the
eastern wall of the town to be sustained. On the contrary, the meander cut-off and the abandonment of the previous river course
would have been able both to enhance the filling-up of such gullies and to accelerate their extinction.