THE EXPLORED ARCHITECTURE. THE VIRTUAL MODEL OF A HISTORICAL STRATIFICATION

The present study deepens -through documents of historical iconography and critical studies on morphological, geometrical and structural aspects- spatial and volumetric relationships between the medieval Torre Pisana of Palazzo Reale to Palermo (also known as Palazzo dei Normanni) and the Astronomical Observatory, site on the summit of the tower. A brief historical and architectural description of the evolution of the tightly correlated structure to the historical-cultural vicissitudes, to the advancement of the scientific theories and to the innovation of the tools of observation and of survey, is a deepening of knowledge for the conservation and safeguard of the architectural testimony. The transformations of the underlying Torre Pisana, which developed over a period of almost nine centuries, are closely related with the ancient Palazzo Reale, that today is a precious architectural palimpsest, a witness to the historical vicissitudes of the city of Palermo. The history of the most salient changes of the turreted palace and especially of the tower, which will host the Astronomical Observatory during the eighteenth century, through the testimonies written of researchers, brings us back to the VI-V century a.C, when, in the highest point of punic Panormo, a military structure was built to defend the western wall of ancient urban settlement. The inside spatial medieval conception of tower’s places is found in setting perfectly centric. The cubic central nucleus is divided in height by the two main areas: the Sala del Tesoro and the Sala del Trono dedicated to real audiences. The compositive scheme concludes with a double order of perimeter ambulatories that coats the central halls, this solution is common in French and English Donjonses of great dimensions. Almost all the rooms with a square or rectangular form have wall roofing structures with cross vault to all sixth resting on main masonries or on perimetric arcs. The Observatory, the first institutional example in Southern Italy (the implementation of which involved prominent figures in the architectural landscape which architects such as Lèon Dufourny, Giuseppe Venanzio Marvuglia, Giovan Battista and Ernesto Basile) was specially designed and dedicated to the practice of Astronomy, where it was and it is possible to make regular observations of celestial bodies. The project of the volumetric configuration of the Observatory compiled respecting local alignments of the vertical wall of the tower, presumably for reasons more oriented to structural stability rather than a geometric and formal continuity. The digital model’s creation of the Astronomical Observatory and the underlying Torre Pisana allowed to mature, through the overlap in levels transparently in plan and in elevation, a greater awareness of the spatial and volumetric interrelationships between typological existing systems, it allowed to identify issues and constructive techniques and to make critical remarks motivating a taxonomy for chronological and constructive criteria. These two deeply different buildings for epoch, for material and for constructive techniques, in static-structural balance, they have, in time, indissolubly linked "fragments" of History, of Art and of Technology that they tell the becoming of the city of Palermo.