Marmore bridge, Steel arch bridge near Marmore Falls in Terni, Italy

The Marmore Bridge is a steel arch bridge on the Terni-Rieti expressway (SS 79 bis Ternana), spanning the Valnerina valley including the Nera River in a single 167-metre main arch. Its deck, 12 metres wide, is supported by two inclined steel tubes of 2.2 metres diameter, braced with Saint Andrew's crosses. The bridge stands 70 metres above the valley floor and is illuminated at night.

A fast road between Terni and Rieti was approved by CIPE on 20 January 1970, but the route was long disputed: a 1977 ANAS plan for an eastern route drew protests over its impact on the Marmore Falls, a southern route was adopted in 1985 and tendered in 1991, then abandoned. The eastern route was confirmed in 2000; the preliminary design was approved on 11 November 2000 and the final design by CIPE on 19 December 2003. The bridge opened to traffic on 12 December 2013 with the 10 km Terni-Rieti section.

The bridge takes its name from the nearby Marmore Falls, whose waters drop nearly 200 metres between the Nera and Velino valleys, the same height difference the viaduct crosses in a few kilometres. Its 170-metre steel arch, assembled from welded prefabricated segments, is lit at night by metal-halide and LED lamps made by AEC Illuminazione, visible from far off.

The bridge carries the SS 79 bis Ternana over the Valnerina near Papigno, in the Terni municipality; it is a road viaduct, not a footbridge, so it is seen from outside rather than crossed on foot. The Nera river and the SS 209 Valnerina pass beneath the single 170 m arch. During bridge maintenance, traffic on the SS 209 is diverted onto a 500 m bypass through the Fondovalle Nera tunnel, with alternating one-way flow.

The bridge's two steel arch tubes, 2.2 metres in diameter, can be walked through for maintenance, a solution described as unique in Italy and abroad. The arch rests on a concrete abutment on the Terni side and directly on the mountain on the Rieti side.