Milan was a centre for the manufacture of arms and armour, and during the 1480s Leonardo sketched many designs for military machines. Some of these may have been conceived as illustrations for a treatise on warfare. The scene here is a military storeyard or arsenal, with piles of gun barrels, cannonballs, a mortar, ladders and lances, and teams of men struggling with levers and pulleys to winch an enormous siege cannon off its bogie.