Excavating a great ditch: the labour and arithmetic of moving earth
Shovelfuls per hour, relays of 14 workers, and the coming survey of barrows, carts and hoists
A large drawing of a great ditch or embankment fills the upper sheet, its slope raked with hatching that stands for earth being cast up from below; the excavation is measured at 40, 12 and 32 braccia. The surrounding notes reckon the labour of digging: a good workman handles some 400 spadefuls an hour of roughly 10-pound loads, thrown six braccia and relayed through the hands of 14 men before reaching the top, with volumes weighed in cubic braccia and cubic canne. Marginal remarks note that men on the level throw more than those on a slope, and promise a coming account of the devices for moving spoil — hand-barrows, wheelbarrows, carts, rope- and wheel-machines, falcons and pontoons. Dense columns of arithmetic below and above the drawing work the figures out.
On this page
The great ditch and its relay of diggers
The main drawing shows a great ditch (fossato) with its dimensions marked n, 40 braccia, 12 braccia and 32 braccia. A shovelful of earth, before it is raised to the top of the mound, passes through the hands of 14 workers, each digging in front and throwing behind over a span of six braccia.
Output and weight of excavated earth
A sustained workman handles 400 shovelfuls per hour of about 10 pounds each; 180 shovelfuls make one cubic braccio, and one cubic braccio weighs 1800 pounds. A cubic canna holds 64 cubes and weighs 115,200 pounds, filled in 28 and 2/5 hours — reckoned as 2 and 1/2 common days, or five half-days per canna.
From hand-barrows to carts, ropes, wheels and pontoons
Because men throwing uphill spill earth along the way, especially when it is too muddy or too dry, hand-barrows (barelle) were devised. After stating their shortcomings Leonardo promises to treat wheelbarrows, then carts, then instruments with ropes, then with wheels and 'falcons' and pontoons and innumerable other devices.
Columns of calculation around the drawing
Grids of figures above and below the ditch multiply the basic rates — 1800, 400, 64, 180, 576 and the like — converting shovelfuls into cubic braccia and cubic canne and counting shovels per square. A note reads that at 20 ninths per hour one digs a canna.