Trachytes Used for Paving Roman Roads in the Po Plain: Characterization by Petrographic and Chemical Parameters and Provenance of Flagstones

Main Roman roads ( Viae publicae silice stratae) in the Po Plain were paved at segments with flagstones, which in places are still preserved in their original position. More frequently, however, the flagstones were removed and transported to museums, dispersed around the area or, in places, interred after archaeological investigation. Those flagstones are made mainly of trachytes from the Euganean Hills (close to Padua, in Northern Italy), a magmatic Complex of Tertiary age, comprising trachytes, rhyolites, dacites and subordinate basalts. The Euganean trachytes were used intensively, starting probably from the Palaeovenetian times (seventh–sixth centuries bc ), and particularly under the Romans, when they spread in Northern Italy from Pavia, to Brixen and Aquileia, down to central Italy, as far as Fano (Pesaro province), mainly for paving roads. In order to determine which, among the more than 70 quarries opened through time in the Euganean trachytic bodies, provided the flagstones for paving the Roman roads in the Po plain, 269 flagstones were sampled and compared petrographically and chemically with the trachytes of quarried localities. It is concluded that the flagstones were provided by three localities: mainly Monselice and, subordinately, by Monte Merlo and Monte Oliveto; flagstones from other localities (Monte San Daniele, Monte Rosso and Monte Trevisan) are very rare. All localities lie along the eastern border of the Euganean Hills, whereas the trachytic bodies of the western border, were not exploited. Probably the flagstones sources were close to transportation routes and in particular to the network of lagoon canals connecting those quarries to the Adige river, which in the Roman times flowed close to the southern offshoots of the Euganean Hills.