Petrary

Petrary is a generic term for a medieval stone-throwing siege engine (from the Greek "petra", "stone"), used to hurl large rocks against the walls of the besieged city, in an attempt to break down the wall and create an entry point.

Petraries can be either gravity operated, where a large counterweight drops to propel the missile, or tension operated, where the throwing arm is pulled back against twisted rope or animal sinew, which then provides the power when released.