During the 1480s, Leonardo seems to worked on a treatise on machines of war. This drawing shows a number of designs for gun-barrels and mortars. At the bottom of the sheet is a huge box-shaped mortar mounted on a rather unstable boat (which would probably have capsized when the mortar was fired). By contrast, the long gun-barrels at upper centre were conceived as fine pieces of engineering. The turntable at the centre of the sheet is a cradle for mounting the gun above, with two opposed barrels so that one could be loaded while the other was fired.