Il disegno del sottosuolo: la Grotta della Sibilla di Marsala nel Voyage pittoresque di Jean Houël

The representation of the underground is a subject of great complexity and a challenge for the disciplines of representation: the topological dimension prevails over the control of the gaze, which is limited to the immediate surroundings of the observer.The peculiar features of underground spaces, e.g. continuous changes of direction and elevation, and poor illumination, have made surveying operations extremely complex; static laser scanners, capable of documenting the morphology of surfaces even in total darkness, offered an initial effective response to such difficulties. In more recent times, mobile mapping systems, which allow the sensor’s path to be ‘tracked,’ have allowed the rapid acquisition of digital twins, which accurately register the morphological features of hypogeal environments. Digital twins, however, do not solve by themselves the problem of the representation of the underground. Many drawings from the past that, even when not referred to a specific location, are capable of representing the peculiar features of the underground, result even more effectively than mimetic digital twins. A retrospective study can therefore help to find solutions that overcome the seduction of mute mimicry. The paper investigates the proposed theme starting from the analysis of a drawing made between 1776 and 1780 by Jean Houël, a Grand Tour traveler, to illustrate a hypogeum with strong mythological values, the so-called Sybil’s Grotto in Marsala, in the province of Trapani.