Bridging a seasonal torrent: The Melfa river,southern Lazio,Italy

The Melfa River is a torrent of the intramontane Lower Liri Valley, which has been a difficult barrier to cross since ancient times. It is dry and can be forded during the summer, but it experiences high floods during rainy reasons, with recurrent disruption of bridges. In Iron Age and early Roman times, fords and bridges were located near the confluence of the river with the valley plain, servicing the ancient Via Pedemontana. Later, faster routes with bridges were moved toward the flatter central area of the valley. There, Romans selected a crossing through wide braided reaches, taking advantage of fording, but consistently losing low lying, long bridges. Traces of one and possibly two such bridges remain along what was the Via Latina, from Fregellae to Aquino. For such bridges, the Romans used relatively strong piers, probably linked with readily detachable (by floods) and replaceable, wooden, flat roadways. The strategy of Medieval and Modern civilizations was instead to bridge the river in a more permanent way, with arches across the nearby deep gorges whose banks are composed of stable calcareous conglomerates and sandstones.