Excavating the ditch of Monte a Santa Maria in live rock
Reckoning the fortress ditch, its two walls and parapet, and repricing rock excavation at 2 ducats the canna
This verso continues Leonardo's costing of the fortress on Monte a Santa Maria. He measures the encircling ditch (17 braccia wide, 16 deep and 640 long) as 2720 canne of excavation, then argues that because it must be cut through live rock handled a dozen times over, the earlier price of 5 lire the canna is untenable and no master could do it for less than 2 gold ducats the canna, giving 5440 ducats. He adds the two side walls of the ditch at 1280 ducats and the parapet at 450 ducats. A short column at the foot sums the figures, reaching 7170 ducats.
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Excavating the ditch through live rock
The ditch encircling the fortress, 17 braccia wide, 16 deep and 640 long, gives 174080 braccia, which divided by 64 make 2720 canne. Leonardo revises the earlier contract of 5 lire the canna (which covered only loosening the stone) to 2 gold ducats the canna, since most is live rock that must pass through more than twelve handlings, so the excavation comes to 5440 ducats.
The two side walls of the ditch
One wall of the ditch, 640 braccia long and 16 high, is 10240 braccia, or 640 canne; the opposite wall is equal, since the 640-braccia length was taken at the middle of the ditch. Doubling 640 gives 1280 canne, so 1280 ducats at one ducat the canna.
The parapet wall
The parapet, a smaller circuit than the 640 at the middle of the ditch, is taken at 600 braccia long, 2 high and 6 wide. Width by height is 12, and 12 by the length 600 gives 7200 braccia, which divided by 16 make 450 canne, that is 450 ducats.
Summing the fortification costs
The column at the foot adds the three totals, 5440 for the excavation, 1280 for the walls and 450 for the parapet, to a grand total of 7170 ducats, with the further figures 2528 and 4642 worked alongside.