The Etruscan tunnel called Ponte Coperto is located NW of Rome, near the town of Cerveteri. The Ponte Coperto tunnel, mapped for the first time during the present research and dug mainly in volcanic tuff lying below the lava flow, was built to drain a valley of about 8.5 km2, probably between the VII and VI century B.C. Before the tunnel construction, part of the valley was occupied by a swamp, whose reclamation was carried out by digging a long rectilinear canal of about 800 metres to the tunnel opening. Several hundred metres upstream of the tunnel entrance a secondary canal flows into the main one; this tributary canal drains a secondary valley, next to the principal one. Nowadays the Ponte Coperto tunnel, 170 m long, looks much larger than its original shape due to natural erosion that has widened and deepened it: during the dry season its discharge is negligible, but some calculations show that the peak discharge can be in the order of several dozens of cubic metres per second. The efficiency of the Ponte Coperto system is outstanding, as the hydraulic setup of the area is still that left by the Etruscans engineers more than two millennia ago: the tunnel and the canals keep draining both the surface and the ground waters from the more permeable rocks, and the valley is still healthy and cultivated. The Ponte Coperto system is a good example of the fact that Roman water engineering has its roots in Etruscan technology.

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