This formal drawing shows how a fortress wall may be breached and the bailey within subdued. Four mortars outside the walls rain stones into the fortress, while a section of wall has been undermined and has fallen into an inner ditch. Cannon placed on earthworks either side of the breach direct their fire into the fortress. Inscribed, upper left corner, Melzi's number 187. Compare 912337 verso, showing a very similar arrangement, from the time of Leonardo's early work on the Battle of Anghiari, and thus c.1503-4; another in the Codex Atlanticus, 24r-a.

Leonardo had a longstanding interest in military theory, and may have considered writing an illustrated treatise on the subject. The vulnerability of the high medieval curtain wall to cannon fire, following the introduction of gunpowder to Europe in the fifteenth century, led to the development of low, thick ramparts, with projections (bastions) to allow defensive fire in all directions.

Text adapted from Leonardo da Vinci: A life in drawing, London, 2018