A drawing of the courtyard of a foundry: in the centre stands a crane by which the barrel of a large gun is being hoisted on to a gun-carriage; to the right and left, nude men strain to raise it; mortars are ranged in the background, along with a gun-carriage, cannon-balls and joists of wood. During the 1480s Leonardo lived in Milan, Italy’s leading centre of arms manufacture. His many military drawings of the period suggest that he dallied with the idea of writing a treatise on weaponry, to which this drawing may have been envisaged as an illustration. Teams of nude men struggle to take the weight of an enormous siege cannon, of a type that was then a speciality of eastern European and Ottoman foundries, weighing many tons and firing huge stone cannonballs.