Gastraphetes were invented back in ancient greece, Da Vinci drew everything else we have used, so why not say he made his own drawing of one... but this was invented around 400 b.c. so I dont think Da Vinci would have invented it 1900 years after that. The Gastraphetes is considered the first "artillery" as it shot large bolts, and was more of a machine than a tool.
Though I than He - may longer live
He longer must - than I -
For I have but the power to kill,
Without--the power to die--
The only reoccurence in every AoM games you lose, is you.