Just a few months after an extremely rare Rebuplican-era Roman bridge was discovered over the Fosso di Pratolungo tributary of the Aniene River in northeastern Rome, a second, much later bridge has been found less than 100 feet away. Archaeologists have been excavating the route of a planned enlargement of the Via Tiburtina within the municipality of Rome. They found the recently-discovered bridge on the opposite bank of the tributary from the Republican bridge. Its precise date is unknown, but it is from the Imperial era.
The bridge on the ancient Via Tiburtina crossed the Fosso di Pratolungo right before its confluence with the Aniene. Excavations brought to light the central span of the bridge, a rounded arch made out of massive blocks of travertine. They were laid dry, using no mortar, joined together by rectangular projections on one block fitted into matching rectangular grooves on the adjacent block. The exterior was then reinforced with a layer of concrete.
The arch is missing its keystone. Archaeologists believe it was likely cadged in the Middle Ages when the bridge was partially demolished and enclosed by two walls 10 feet high coated with a layer of plaster on the exterior. The walls appear to have supported a ramp used to cross the tributary.
The analysis of the historical cartography of this area highlights the convergence of several branches of the Fosso and of small tributaries, the course of which varied according to the eras. The stratigraphy then highlighted the remarkable alluvial layers that attest that the bridge crossed the Fosso at a critical point, subject since Roman times to frequent flooding and swamping phenomena.
The remains of the bridge will be protected and reburied as they are 13 feet below street level inside an aquifer and therefore cannot be moved. The expansion of the highway will not damage the archaeological material.