Theory and technique in the preservation and evaluation of an archeological site. The case of the new excavations at the level of the lower basilica of S. Clemente in Rome

Since 1981 an area underlying the convent which adjoins the basilica of S. Clemente in Rome has been subjected to a number excavation campaigns. The latest excavations (2006-2011) involved a portion of the convent garden adjoining the north aisle of the lower basilica. These have brought to light some structures of the 3rd century AD building, a building which later housed a Christian church and which still later was to be transformed into an early Christian basilica. The general instability of the structure and the decay and deterioration arising from severe microclimatic factors in the excavated area gave rise to a series of problems. In 2012 initial works were undertaken to ensure the safety of the site while allowing for a more permanent solution to be projected. The idea was simple: it was necessary to avoid any additional structure which would cause any thrust on the surrounding ground or indeed transfer it elsewhere. What was needed then was to make the wall 'self-supporting', i.e. capable of absorbing the strains without deforming itself too much or triggering any other unwanted effect. The solution consisted of a series of steel beams placed against the wall which needed to be supported. These were fixed to adjacent transversal structures by a recessed or chemical anchorage. The support structure was adapted to the irregular masonry by filling with thixotropic mortar, chromatically harmonised with the ancient surfaces. In addition to this new structure, some complementary operations were carried out, such as: waterproofing, thermal protection and microclimatic control, consolidation and restoration of ancient surfaces