The Citadel of Turin: geometric design and underground archaeological evidence

The Citadel of Turin, designed by Francesco Paciotto and built from 1564, is one of the first and most famous examples of pentagonal modern fortification. The new fortress, whose design is featured by the rigorous concatenation of defensive elements that expresses the close link between architecture, geometry and ballistics, became operative since 1566, with the placement of the first artillery. For over two centuries it was the fulcrum of Turin defences, finally unarmed and largely dismantled during the second half of the 19th century. However, the lower sections of main defences and detached works were spared and buried inside the filled ditches, as well as the underground countermine system. Significant six and eighteenth-centuries drawings, which document the succession of interventions to build the belt of external defences between the siege of 1640 and the early 18th century, and one of the first half of the 19th century, just before the partial demolition of the above-ground parts, were selected. They are the object of graphical analysis through digital re-drawing, aimed to hypothesize the geometric criteria that rules the subsequent construction phases, and to relate the designed fortification with the archaeological evidence, today the subject of systematic recovery, study and enhancement from the Fifties of the 20th century.