Natural vs built environment: integrated methodological approach for reconstruction of connections between urban transformations and natural environment of the ancient Tursi Rabatana citadel, S. Italy

Tursi and its medieval citadel called "Rabatana", located to the top of a sandyclayey hill, is one of the most representative sites of the cultural heritage of Basilicata region, southern Italy. In spite of this, the historical origin of this small citadel characterized by an Arabian toponym is still now not well defined. Historically the first phase of life of Rabatana's citadel is deeply connected with caves excavation along the steep slopes of the hill, used as shelter for men and animals as well as part of a hydraulic system to collect water in cisterns. The interaction during the last centuries between anthropic activity (caves excavation, birth and growing of a built-up area and following recent desertion of the settlement) and the characters of this natural environment have been the reason of a progressive increasing of the hazard and vulnerability levels of this site. In order to reconstruct the complex interactions of the last ten centuries between the natural and the built environment of Tursi-Rabatana site an integrated methodological approach has been carried out. Urban form, individuation of the settlement's location as well as all that belongs to the anthropic activity is the expression of the military, religious, artistic and technological culture of the age in which it is designed and realized. Stylistic features, building and hydraulic techniques and functional aspects change in time often modifying the link that each settlement has with the environment to which it belongs. Integrated analysis between historical documents, (urban structure and its evolution, building and hydraulic techniques) territorial data and a geophysical survey has been carried out in order to understand the meaning of the labyrinth of interconnected and overlapped ancient buildings to hypogeal structure, such as cisterns, crypts and caves, with respect to the urban origin and development, as well as the present risk level of the settlement. The geophysical investigation, combining the Electrical Resistivity Tomography (ERT) method with the Ground Penetrating Radar (GPR), permitted to map shallow cavities and tunnels in the subsurface giving a contribute to better reconstruct the hypogeal environment excavated in the shallow sandy layers. The work also evidenced as the ancient hydraulic systems, now almost completely forgotten, used to collect and store water inside the urban area, as well as the morphoevolutive processes linked to the lithology of the substratum and rainfalls have been determinant for increasing the risk level.