Medieval phases of settlement at Benabbio castle, Apennine mountains, Italy: evidence from Ground Penetrating Radar survey

The lack of written sources for many of the medieval castles in the northern Apennines (Italy) makes it difficult to completely establish the most ancient historical phases of these settlements. The church of San Michele belongs to an abandoned fortified settlement of the Castle of Benabbio, in the mountains surrounding Lucca. Thanks to an epigraph still visible on the façade, the church foundation is dated back to AD 1218. However, several archaeological findings at the settlement seem to suggest stages of encastlement that are older than the church foundation.A Ground Penetrating Radar (GPR) survey has been carried out in the inner part of the church in order to identify the presence of pre-AD 1218 buried structures. A 0.5 m grid was used to acquire GPR data over the entire pavement of the church, using an antenna of 200 MHz of nominal peak frequency. A standard sequence of raw data processing was adopted, and the interpretation was performed both on vertical radar profiles and time-slices.The distribution of areas of high back-scattered electromagnetic energy shows regular patterns with orthogonal alignments archaeologically compatible with buried stone walls. In the western sector of the church, the subsurface structures are consistent with the wall remains of a building which, due to its size and shape, is unlikely to have been used for religious activities. This building can be related to an 11th–12th century encastlement of the site. The other structures detected by GPR prospection can be referred to the construction of the 13th century Romanesque church, while its Renaissance enlargement may have taken place in the late 15th century. During this last phase, a hypogean room was excavated near the altar and probably used as crypt/ossuary.The results of this multidisciplinary work have supported some archaeological hypotheses concerning the architectural history of the church, dating back to the 11th–12th century, when the first stone structures of the Benabbio castle were erected.