"Here every blow diminishes by half, because it is delivered in between"
This model represents a section of fortified
curtain wall subdivided into three fundamental
elements: the escarpment, the salients or spurs,
and the covering. It was constructed on the
basis of interpretations of a group of drawings
executed by Leonardo during the months
he spent in service to Cesare Borgia. The escarpment was designed according to canons proposed by Francesco di Giorgio Martini: it is steeply inclined to deflect strikes by enemy artillery and with a pronounced ratio between horizontal and vertical extents to provide maximum structural resistance against frontal strikes from enemy fire.
The semicircular salients also were designed for
resisting the force of collisions and demonstrate
how Leonardo was making use of his recent
studies of ballistics in designing convex forms
to offer the least possible incidence for incoming
missiles. In his note on folio 50v, he writes: Here
every blow diminishes by half, because it is delivered in between. The profiles of the salients are constituted of courses of bricks arranged radially so as to distribute lateral loads and thrusts.
This observation demonstrates that he had well
studied resistance in arches in previous years.
The batteries of artillery are positioned in the
voids between one salient and the next.
The broad vacant spaces are recessed at the
back of the covering, which is parabolic in form
to resist both horizontal and vertical blows.
And finally, the covering conceals the drop holes,
which are designed for defending both the front
of the fortress and the accesses behind the
embrasures. This architecture, with its revolutionary forms and which shapes itself around the physical phenomenon of the incidence of projectiles, would appear to have been designed by
Leonardo according to criteria of a purely passive defense.
The model is based on the drawing:
- Manuscript L ff. 50 v., 63 r. (1498-1502)
Paris, Institut de France