The Citadel of Turin: geometric design and underground archaeological evidence

The Citadel of Turin (1564) is one of the first pentagonal modern fortification. For over two centuries it was the fulcrum of Turin defences, finally unarmed and largely dismantled during the second half of the nineteenth 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 historical drawings, documenting the building of external defences are selected aiming to recognize geometric criteria that rules the subsequent phases, and to relate the designed fortification with the archaeological evidence.