Its name is Ponte del Toro because it has always been thought that the archway a few feet away from Marmore Waterfall was the ruins of a much larger structure, to be precise, a bridge built in Roman era. Instead, even though the building technique is the same as that of Roman bridges, it is a structure used for hydraulic regimentation, This was ascertained during recent restoration works and the rediscovery of a manufact that had been covered by dirt and brambles for years. It had been identified at the beginning of the 19th century during the construction of the intake structure of one of the many canals that took water to Terni. In the same area, on the opposite side with regards to the river Nera, a prehistoric settlement came to light.
It was possible to better understand what the real function of the structure was after a search for the missing parts and a long-awaited study carried out on, it is not wide enough to be compatible with a road and, furthermore, the upstream side ends against the rock outcrop. It remains, however, a monumental construction, built with large blocks of sponge stone, the same stone that obstructed, partially but consistently, the light of the arch. Sponge stone is a travertine that forms rapidly through the calcification of leaves and organic debris. According to some theories, the structure regulated the flow of the Nera and the lake that had formed upstream consequent to the realisation of Marmore Waterfall, but there is no record of the existence of that lake at the time Ponte del Toro was built, round about the time Christ was born. The present day accredited hypothesis is, therefore, that it was used to contain and regulate the flow of the waters from the Marmore plateau ( and in a period prior to the realisation of that stupendous hydraulic work, the Waterfall) precipitated into the river Nera running along a natural canyon along the steep side of the mountain overhanging the valley. A canyon that can still be seen among all the vegetation, on the left side of Ponte del Toro ( the right side for who is standing in front of it) and points down to the spot where the work was built.