Fortress Studies: Ravelins, Wells and Ricochet of Shot
Circular plans and sections with rules on ravelins, mines and the bounce of cannonballs
This crowded sheet develops a circular-plan fortress ringed by ravelins, drawn both in plan and in section with domed casemates, bridges and the lines of artillery fire. The notes argue that a ravelin must fully encircle the fortress to be safe, that a mutual defence must hold between fortress and ravelin, and that deep wells around mountain fortresses guard against undermining. Small diagrams at the upper right classify the rectilinear and curvilinear bounces (balzi) of a shot, and a long note analyses how a ball ricochets along the angle between wall and ground. Additional untranscribed writing appears across the sheet.
On this page
A ravelin must encircle the whole fortress
Leonardo concludes that any ravelin that does not run entirely around the fortress can be attacked within itself. The ravelin, called the shield of the fortress, must be as well defended by the fortress as the fortress is by it, and the garrison's chambers are to be partitioned with boards.
Deep wells against undermining
At mountain fortresses many very deep wells should be sunk all around, outside and within, so that underground fires (mines) cannot overturn the walls. A further note asks that a relief force be admitted through the keep into the town without entering the fortress, and be shut up as prisoners at the castellan's pleasure.
Impact is weakest on an oblique surface
That impact will be of lesser force which is delivered upon an object of greater obliquity. The reciprocal rule of fire follows: by as many lines as the defender can strike his attacker, by so many the attacker can strike the defender.
Ricochet of a ball along the wall angle
If the ball is fired along the length of the angle formed by the wall face and the ground that sustains it, it follows its course in continuous contact with that angle. If it strikes into the angle it rushes rectilinearly from one face to the other until its fury is spent; and if fired downward toward the angle its motion is doubly rushing, one part rectilinear and the other curved. The upper-right diagrams label these paths as rectilinear and curvilinear bounces (balzi), curved line and straight line.
Fortress and casemates seen in section
The centre of the sheet shows the fortress in section as a broad domed and vaulted mass of arcaded casemates, flanked by a bridge or gateway, while several circular fortress plans are ruled with radiating lines of fire. Beneath one is written the note 'For giving fire'.