What is "gastraphetes"

The gastraphetes (from Ancient Greek γαστραφέτης, English translation: "belly-releaser") was a hand-held crossbow used by the Ancient Greeks. It was described in the 1st century AD by the Greek author Heron of Alexandria in his work Belopoeica, which draws on an earlier account of the famous Greek engineer Ctesibius ( fl. 285–222 BC). Heron identifies the gastraphetes as the forerunner of the later catapult, which places its invention some unknown time prior to c. 420 BC.

Unlike later Roman and medieval crossbows, spanning the weapon was not done by pulling up the string, but by pushing down an elaborate slider mechanism.