“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 as a distinctive class eligible for protection. After a critical overview of previous attempts at defining underground heritage by associations such as UIS, SSI and UNESCO, this article updates the definition of the new-born class of UBH on the basis of three main criteria: position (by introducing the concept of Geographical Zero Level), manmade character, and cultural relevance, both material and immaterial. Building on the outputs of several projects devoted to this topic and the results of academic expertise in this field, the author proposes a new dedicated methodological approach consisting of a chart for the classification of artefacts as historical UBH and a strategy for their reuse based on a four-level scale: Re-inventing, Re-introducing, Re-interpreting and Re-building.