The model represents a section of a fortification with moat, over which is positioned an adjustable ladder equipped with rollers allowing soldiers to position themselves behind enemy walls and scale them over the moats. The ladder with rungs could be adjusted for inclination by means of gears composed of a toothed wheel and endless screw. The drawing in the Codex Forster I can be related with another coeval drawing from the Codex Trivulzianus, in which Leonardo also drew a section of the fortress being attacked.
The model is based on the drawing:
- Manuscript L f. 46 v. (1487-1492)
Paris, Institut de France