Towers in Deep Water, Counter-Mines and Ditches
Water-set towers to defeat sappers; wide dry ditches and timber-woven walls against artillery
Folio 92r continues the fortification treatise from 91v. Leonardo argues that flanking towers should stand in deep water within and without so enemy sappers can find no firm footing, keeps their embrasures scarped inside the wall's thickness, and describes secret counter-mining beneath the ditch water with the spoil hidden in gardens, cellars and ground-floor rooms, preferring a solid-cored tower ringed by internal streets. A further note calls for wide, deep dry ditches, which are harder to bridge or scale and more terrifying to escaladers than water because a man cannot catch hold of anything as he falls, together with wall-thicknesses woven with timber so that bombards cannot bring down large sections at a single blow. A profile of a round bastion with a ramp is labelled ditch, square, houses.
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Towers set in deep water against sappers
The towers that fire through their underground rooms along the streets are set in deep water inside and out, so that if the townsfolk try to reach the tower-bottoms by mine they find no firm ground to stand on. Their embrasures lie in the thickness of the walls, scarped both toward the tower's center and outward.
Secret counter-mining and concealment of spoil
One digs beneath the water of the ditches and props the roof so the water-bottom does not sink the earth above the cut. Such caves are made in secret, and the excavated earth is used to fill the gardens, cellars and ground-floor rooms of the houses where the digging began; better still to leave the tower solid at its core with the streets running around the mass.
Wide, deep dry ditches and wet-hay defenses
Ditches should be wide so machines cannot bridge them, and deep so the walls stay too high to scale; the bottom should let fascines and timber be set alight if the enemy tries to fill it. Wet wool bales, sea-sedge and wet hay screen the flanks against artillery, and a broad waterless ditch terrifies escaladers, who fear the fall to bare earth more than into water where they might catch hold and float.
Wall-thicknesses woven with beams
The thickness of the walls should be interwoven with beams so that the bombards cannot throw great pieces of them to the ground at a single blow.
Profile of a round bastion (ditch, square, houses)
A profile sketch shows a round bastion or tower with a ramp or bridge running up to it. The drawing carries the words ditch, square, houses, keying its parts.