Cost of Excavating the Fortress Ditch and Foundations
2720 canne at 5 lire = 4662 6/7 ducats; total with foundations 4834 2/7
Leonardo reckons the cost of the fortress earthworks: the 2720 canne of excavation come to 32640 lire, that is 4662 and 6/7 ducats, before the digging of the fortress foundations (about 240 canne at 5 lire = 1200 lire, or 171 3/7 ducats), which together make 4834 and 2/7 ducats. He adds that the walls of the ditches and the arched pillars beneath the fortress walls are not yet counted. Sketches of a hoisting/excavation mechanism accompany the columns of arithmetic that carry out the sums.
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Excavation and foundation volumes of the fortress
The 2720 canne of excavation are priced out, then the foundation trench of the fortress, running one canna deep and one and a half canne wide at least (about 240 canne), is added at 5 lire the canna. The passage keeps the fortress ditch and its rock as a works-on-site problem.
Running total in ducats; items not yet counted
The account closes at 4834 and 2/7 ducats and notes what is still left out: the walls of the ditches and the arched pillars that stand beneath the walls of the fortress, "of which I make no mention."
Hoisting and excavation mechanism
Sketches show a pivoting boom or crane arm and a framed device with an inclined chute, mechanisms for lifting and moving spoil out of the deep ditch. They are drawn amid the cost figures rather than dimensioned in detail.
Columns of calculation
Stacked multiplications and divisions down the left side carry the figures: 2720 by 12, the product 32640, its reduction to 4662 6/7 ducats, and 240 by 5 giving 1200 (171 3/7 ducats), summed to 4834 2/7.