Dimensions of the Fortress Ditch and the Files of Diggers
17 by 16 by 640 braccia = 174080 sq. braccia = 2720 canne at 5 lire
Leonardo works out the whole excavation of the ditch: 17 braccia wide, 16 deep and 640 long, which reduces to 174080 square braccia, or 2720 square canne, priced at 5 lire the canna because of the difficulty of the rock, as was formerly allotted to the diggers. He notes that at such shallow width each digger could cast the earth clear without moving and left the loosened stones at the bottom for the foundation masonry. But once the cut is 16 braccia wide, four files of men are needed, and the rows toward the embankment must be doubled, so that six files in all are required. Marginal number columns and small diagrams of ranked men and a stepped trench accompany the text.
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Volume and pricing of the whole ditch
The ditch, 17 braccia wide, 16 deep and 640 long, reduces to 174080 square braccia, i.e. 2720 canne, valued at 5 lire the canna for the hardness of the rock. In shallow cuts each digger casts the earth clear without shifting and leaves the loosened stone at the bottom for the foundation masonry.
Reductions to square canne and rates a and b
Column sums carry the dimensions to 174080 and its reduction to 2720 (also written 2728) canne, with a note that a is 10 lire and b is 20 lire. Further stacks (160 x 4 = 640; 16, 17) work the widths and depths.
Doubled files of men for the wider cut
When the excavation is 16 braccia wide, four files are needed, the two inner ones relaying earth to those by the bank; and because the bank rows must be doubled, six files of men are required in all.
Diagrams of ranked men and a stepped trench
Small framed sketches show rows of little figures set in files, and a lower diagram of a stepped, terraced trench, illustrating how the diggers are ranged at successive depths.