Although he regarded war as a "most bestial madness", Leonardo devoted a significant part of his studies to analysing arms and war machines. The contradiction is more apparent than real, when it is borne in mind that he spent his life in the service of the most important lords of the times and, for many of them, warfare, whether actually fought or solely as a preventive measure, was inseparable from holding power. It is no coincidence, therefore, that in the famous letter of introduction in which he offered his services to Ludovico il Moro, Duke of Milan, Leonardo particularly emphasised his gifts as military engineer and arms designer.
The arms he designed for the duke were mainly firearms but there were also siege machines, catapults and suchlike, which hark back to more traditional warfare. In any case, the introduction of gunpowder during the fourteenth century, did not immediately entail the disappearance of earlier weapons. Swords and firearms were used together for a long time and both were studied and improved by the experts of the time. Imagination played an important part in Leonardo's makeup, as his beautiful, fanciful designs for clubs and lance heads show, as well as his Machiavellian project for a multiple crossbow for rapid successive firing. Alongside this fantastical side, which led him to create designs that were sometimes unworkable, there nevertheless emerges a constant striving not so much to design new weapons but to improve and perfect the efficiency of existing ones, both traditional and firearms.
This ambition is clear in one of his most spectacular projects for a giant crossbow, designed as a transportable field weapon, and probably intended for knocking down defence walls by firing heavy balls of stone. Outsize crossbows were in use at the time, although using the more traditional arrows, and could be as long as five metres with a cross-section of up to twelve centimetres. Leonardo's crossbow seems even more powerful than contemporary ones, and although the length is not specified, it seems to be easily reconstructable in relation to the transport carriage, which is about 23 metres long while the bow span is almost 24 metres. Leonardo also devised ways of making more rudimentary cannons and bombards more efficient by studying their founding, loading, lighting and cooling as well as increasing the rate of fire and speed of firing. He also examined the form and trajectory of projectiles to increase firing accuracy and from his experiments with jets of water, he produced a parabolic curve that anticipated Galileo and Newton's studies of the principle of inertia.