Rocca Nuova, Serravalle Pistoiese

In the ambitious project of «putting the Arno in a canal" from Florence to the Fucecchio Marsh through Prato, Pistoia and the Val di Nievole, Leonardo studies the feasibility of passing through the Serravalle hill in a tunnel. For this purpose, he conceived a leveling tool (Madrid Code I, f. 111 r, c. 1495) to ensure that «starting the aforementioned quarry on each side of the mountain, it would collide together on the same line».