罗马内战
The ballista was a powerful catapult, consisting of a beam with a frame at the end, mounting two rigid arms powered by torsion in bundles of sinew at each side, which would pull a bowstring between them propelling the projectile. It launched heavy darts called bolts, or spherical stone projectiles of various sizes. Ballistas were fit with grappling hooks to seize enemy vessels during the Roman civil wars. The Romans would develop an improved version with inward facing arms in the 3rd century, the remains of such were found in the town of Hatra in Iraq.