The onager was a single-arm, torsion-powered stone thrower described by the 4th-century Roman writer Ammianus Marcellinus.
Its mechanism used twisted rope bundles to store energy. A winch pulled the wooden throwing arm down, a leather sling held the stone, and a release mechanism unleashed the arm. The sling then launched the projectile in a curved trajectory.
The arm's powerful upward movement inspired the name onager, referring to the wild ass's kicking action.
This cinematic 3D CGI weapon breakdown reveals the torsion bundle, single throwing arm, winch, sling and padded stopping cushion through internal camera movements and neon-lit mechanical visualizations.
No complete original onager survives, so its exact construction remains debated. This is a historically informed reconstruction, not an archaeological replica of a surviving machine.
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