The invention of ballista is generally attributed to the ancient Greeks, specifically the Greek engineer Dionysius of Alexandria, in the 3rd century BC. Dionysius is credited with developing various siege engines, including the ballista, during his service under Alexander the Great. However, it is important to note that rudimentary versions of torsion-based weaponry, including early forms of ballistae, may have existed prior to Dionysius' time, potentially originating in earlier cultures.