This catapult model was a design for an improved version of older models sketched by Leonardo da Vinci. His idea was intended to be a more powerful catapult that could be used in warfare. His invention allowed for the ammunition to be propelled at much faster speeds. This was done by the use of a leaf spring, which is a spring that could be more easiy bent and deformed so that it can store more energy and release with more power. Image source: Wikimedia Commons, Catapult from Leonardo da Vinci's "Codex Atlanticus", listed as public domain in the United States because it was published before January 1, 1923.