“Underground Built Heritage”: A Theoretical Approach for the Definition of an International Class

Although nowadays sustainable reuse of underground cultural heritage has become a global trend, as yet Underground Built Heritage (UBH) is not regarded distinctive class eligible for protection. After critical overview previous attempts at defining by associations such UIS, SSI and UNESCO, this article updates the definition new-born UBH on basis three main criteria: position (by introducing concept Geographical Zero Level), manmade character, relevance, both material immaterial. Building outputs several projects devoted to topic results academic expertise in field, author proposes new dedicated methodological approach consisting chart classification artefacts historical strategy their based four-level scale: Re-inventing, Re-introducing, Re-interpreting Re-building.