This drawing is the most formal of Leonardo’s military drawings from the period, its composition derived from a woodcut in Valturio showing a framework and pulley for hoisting a cannon on and off its bogey. The scene appears to be a military storeyard or arsenal with teams of nude men struggling with levers to take the weight of an enormous bombard, closely resembling the siege bombards that were a speciality of Ottoman foundries, such as the ‘Dardanelles Gun’ now at Fort Nelson, Portsmouth (and Leonardo has hardly exaggerated the size). Beyond are more gun barrels lying beneath a pitched roof against the wall of a fortress, with huge stone cannonballs, a mortar, ladders and lances. Melzi's number 58.

Milan was Italy’s leading centre for the production of arms and armour, and soon after Leonardo’s arrival in the city he began to sketch designs for all manner of weapons. His career coincided with the introduction of gunpowder into European warfare, and he drew both the old type of weapon – lances, chariots, enormous catapults and crossbows – and the new – guns, cannon and mortars. It is unlikely that any of these designs was put into practice, and they may have been intended instead for an illustrated treatise on warfare.

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