Multidisciplinary investigations on the Roman aqueduct of Grumentum (Basilicata, Southern Italy)

The Romans built the ancient town of Grumentum during the 3rd century B.C. in the southern part of the Agri
high Valley (Basilicata Region, Southern Italy) near the confluence of the Sciaura stream in the Agri River.
Now it is one of the most important archaeological sites of Southern Italy. In fact, after a period of wars in
this area between Romans and Carthaginians, a great deal of restoration was started in 57 B.C. These works
affected the city walls, public buildings and finally endowed the Roman colony with important infrastructures,
such as the new aqueduct. In this work, we attempt to reconstruct the ancient layout of the Roman aqueduct
of Grumentum. As a starting point, we followed some descriptions from the 19th century, when the structure
was still well preserved. Then, we performed a multidisciplinary geophysical approach to the best preserved
remains of the aqueduct. In particular, the geophysical investigation started with the use of a portable GPS allowing
us to acquire the co-ordinates of the outcropping rests of the ancient structure. Then, we used an optical
pumping magnetometer to perform seven gradiometric maps over a broad area of about 8000 m2. From
the literature descriptions, dating to the first part of the 19th century, we can deduce that the state of preservation
of the Roman aqueduct was much better than the present one. Thus we can hypothesise as the cause of
its fast involution the fact that it was located in the epicentral area of the large destructive earthquake which
occurred in the Basilicata Region in 1857 (Mallet, 1862). To this aim, we performed a first attempt to correlate
the state of preservation of the aqueduct remains with the local seismic amplification by means of the
HVSR (Horizontal to Vertical Spectral Ratio) technique. This survey allowed us to obtain the site amplification
spectra along the aqueduct layout and assess the fundamental vibration frequency of the investigated
structure. The possibility of landslides was ruled out by a careful geological survey. The relationship between
aqueduct path and damage should then be attributed to closeness to earthquake seismogenic fault.