abstract: Starting from the early 16th century, the diffusion of firearms led to important changes in the composition of armies. New machines and measuring instruments became part of the arsenal of war. Sieges were planned on the basis of increasingly correct topographic surveying. The artilleryman became a new professional figure whose technical and scientific capabilities were traced in the Nova scientia of Niccolò Tartaglia. The capitano di ventura, trained in direct, man-to-man combat, gradually gave way to the modern condottiere, sufficiently well educated in the mathematical sciences to achieve his greatest success in fighting at a distance. And the dagger, the indispensable weapon of any solder, was progressively transformed into a compass, the traditional allegorical attribute of Geometry. This technological and cultural change, in which the keys of political and military power were entrusted to geometry, implies an extraordinary convergence of technical and scientific capabilities ranging from perspective drawing to topographic surveying, to calculation and measurement. It was within this context that the first scientific collections were formed at princely courts, places delegated to the collection of ever-new measurement instruments clearly designed as both functional objects and symbols of power.