Le cavità nascoste nei “calcareous tufa” del sottosuolo di Rieti
Author(s)
Date Issued
2020
Type
article
Volume
107
Start Page
357
End Page
382
Abstract
The ancient Roman city of Rieti (Reate), developed on the south-eastern edge of the homonymous plain, almost at the confluence of the Turano River with the Velino. It stood on a small cliff of continental carbonate deposits produced by cold mineralized waters (calcareous tufa), improperly defined “travertines”. These deposits were product in the Upper Pleistocene and then were deeply engraved by the hydrographic network and karsified. Over the centuries, urban development has almost completely erased the traces of the river erosion escarpments that limited the southern slope of the ancient cliff. In this sector, the city is stratified on both sides of the viaduct of the Roman bridge over the Velino, which is the current Via Roma. The viaduct, supported by imposing arches, allowed access from Via Salaria, overcoming a swampy area subject to frequent flooding with a difference in height of 17 m. The remains of the shops and the ancient streets, which from the river port and the banks of the Velino leaned against the arches of the bridge, can be observed in the basement of the buildings that open onto Via Roma and constitute the extraordinary universe of the anthropic “underground Rieti”. But in the subsoil of the central part of the city that rises on the cliff there are also extensive, and little known systems of karst cavities, with large rooms largely remodeled and transformed by anthropogenic action, also used as anti-aircraft shelters during the second war world. These cavities, only minimally surveyed, intersect with the remains of tunnels and hydraulic derivation works connected to the articulated system of canals that evolved parallel to the expansion of the walls, both for defensive purposes and to guarantee strength hydraulics (which fed the numerous mills), and for the water supply of the city. The
canals, the fountains, cisterns and the mills were fed not only by the Velino but also by the Cantaro River. They flowed in the north-eastern part of the city. These canals, as well as the Cantaro River, the River of the Nobles and the “cavatelle”, are now buried and disappeared, but they were present until at the end of the nineteenth century, and they have earned to Rieti the title of “ Venice of central Italy “. This system of ducts and cavities, especially the karst phenomena, constitute a real risk factor. They could give rise to sinkhole phenomena, also
considering the high seismicity of the area, connected to the recent tectonic evolution of the Rieti plain and with some faults classified “active and capable” crossing the urban centre.