This relief model represents a triangular outwork, or ravelin, for the military defence of the entrance to a fortress. Its walls are steeply sloping and are divided into two sectors by a ribbing. The much shorter upper sector shows corbels between small arches and loopholes, for positioning of artillery, alternating with embattlements. The corners of the ravelin are blunted, and on the terrace roof there
is a covered patrol walk and three small service buildings. Rather than a ravelin, this could be a bulwark of bastions that Leonardo may have seen, possibly referring to the stronghold at Ostia or at Civita Castellana, in Lazio, both of which were on plans of Giuliano da Sangallo (Marani 1984, p. 162). The bastions are constituted of steeply scarped curtain walls supported on embankments.
The model is based on the drawing:
- Manuscript L ff. 65 r., 7 v. (1500-1501)
Paris, Institut de France