An important stronghold for controlling transit between Pistoia and Val di Nievole, Serravalle is mentioned in Leonardo's studies in relation to the canalization project of the river Arno from Florence to the Fucecchio Marsh through Prato, Pistoia and the Val di Nievole. The new course of the river, eliminating the bends of the natural one, would have been only apparently longer and would have created a great river communication route able to favor trade and transport from the sea, industrial activities - such as spinning mills, weaving factories, watermills - and military activities in which water, or the deprivation of it, could be used as a weapon against the enemy.
To present the advantages of the canal more convincingly, he frequently recurred to calculations that now seem perplexing. On folio RLW 12279 he calculates, in fact, «56 miles by Arno from Florence to Vico [equivalent to about 92 km, while the real distance today is about 63 km], and by the Pistoia Canal it is 44 miles, and thus 12 miles shorter by canal than by Arno». He reiterates this concept in another note: «By Arno from Florence to Vico 61 miles and by canal 45, that is, 16 miles less».
For the realization of the project Leonardo conceived, around 1503, large and innovative excavating machines (Codex Atlanticus, ff. 3r and 4r [ex 1v-a e 1v-b]), as well as sluices that allowed the boats to overcome the different level of the water courses, and the «way to drill through a mountain» (Madrid Ms. I, f. 111 r, c. 1495) starting at the same time from both sides of the relief to pass through the hill of Serravalle in a tunnel.
He is also concerned about finding the necessary funding, imagining an involvement of the Arte della Lana (Atlantic Code, 127r), and the possible savings on the cost of labor, indicating the period most favorable to the work: «This canal should be made from mid-March through mid-June, because the peasants, being free from their ordinary work, can be had for low wages, the days are long and the heat does not tire them».
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Panoramic view of Volterra
CC BY-SA 4.0 - LigaDue
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Panoramic view of Volterra
CC BY-SA 4.0 - LigaDue