Taranto underground: digital survey and virtual exploration of the hypogea along the Aragonese walls

The downtown of Taranto (commonly indicated as ‘Città Vecchia’, Old City) reserves traces of its millennia-old history. A highly fascinating system of these traces can be found in the underground of this downtown, with countless cave-built spaces. In time inhabitants used to dig into the calcarenite embankment, which was easy to quarry and process. In general, it can be noticed that there are various spaces related to religious functions and burial hypogea all along the Northern side of the settlement, while along the ‘Mar Grande’ (The ‘Large Sea’) side the uses are mainly related to work and market activities, with storerooms, oil mills, grain pits and manufacturing or commercial spaces. This concentration of trade related functions is due to the presence of aristocratic mansions above the walls and of the harbor. In time the border of the town center was well defined by the city walls, apparently emerging from the surface of the water, but based on bank and on the cliffs. The appearance of the walls came from a series of interventions, aimed to improve the military response wanted by Ferdinando D’Aragona. The walls were made delimiting the emerging cliffs and various materials filled the empty spaces between the walls, the natural rock, and the existing constructions. Buildings for any functions rose over this natural/artificial soil before and after the presence of the new walls, incorporating, transforming or bringing the presence of the (so called) hypogean cavities. Despite the completion of the work with the addition of bastions, in XVII century there was a progressive loss of military value of the fortifications. The need for a direct access to the sea from the commercial ‘underground’ activities brought the opening of various passages breaking through the walls. The subject of this study is the section close to the Aragonese walls, where various chambers beneath the buildings have access to the sea. The remarkable number of cavities and galleries are at different levels below the surface, very often they intersect and influence each other, forming what may be perceived like ‘another city’. The present research, proposes the results coming from the digital survey of this system, where lasergrammetry and photogrammetry were essential tools to improve the knowledge about historical stratigraphy and also defining better the relationship between the city and its subsoil. The survey was mainly conducted using 3D laser scanner technology, which has allowed to define a specific interpretation using a specific digital 3D model of the current state of hypogea and the following development of an interactive virtual exhibition.