The Inner Pit, Ravelins and Scarped Turrets of the Ditch
A pit sunk in the ditch, ravelin heights, scarp proportions and machicolations
A text-and-diagram page (folio 96r) continuing the ditch and turning to ravelins and turrets. Leonardo sinks a steep-sided pit ten feet deep in the middle of the ditch that no one can stand on without sliding in, and provides underground tunnels to clear the inner ditch when needed. He sets ravelins low, about level with the ditch-wall tops, so bombards cannot strike them, and gives corridor diameters of 50 to 60 feet and turret heights of 50 to 60 feet with a 30-foot scarp battered one foot for every four or five of height, plus smoke-chimneys for the flanking guns and 9-foot machicolations. A plan of a fort with rounded corner towers is drawn at the lower left, captioned that the angle-towers defend the way of relief.
On this page
A steep-sided pit sunk in the middle of the ditch
In the middle of the ditch's depth Leonardo sinks a pit ten feet deep, thirty feet wide at the bottom and thirty-five at the top. The rest of the ditch floor is sloped so steeply that no one can steady his feet without sliding into the pit.
Ravelins set low beneath the bombards' line
Every ravelin before the fortress gates must be set low, about at the summit of the ditch walls, so the shots of the bombards cannot strike it. Around its foot runs a corridor with its own defences, made in the manner of a scarp.
Turret scarp proportion, smoke-chimneys and machicolations
Corridor diameters run 50 to 60 feet, all solid but for the lower flanking defences; turret heights are 50 to 60 feet with a 30-foot scarp that projects one foot for every 4 or 5 of height. Each flanking defence has a chimney to vent the artillery's smoke so the fire is not hindered, and the turret summits carry machicolations 9 feet high on arched corbels projecting 2 and a half to 3 feet.
Angle-towers defending the way of relief
The caption beside the plan states that this ditch will be everywhere equal and simple, and that the towers set at the angles defend the way of relief.
Drawn plan of a fort with rounded corner towers
A small plan at the lower left shows a compact fortress with rounded towers projecting at its four angles and connecting walls between them, the drawing the adjacent captions refer to. It illustrates how the equal, simple ditch and the angle-towers command the relief route.