Torsion-Powered Engine - Byzantine "alakation or ballista"

This weapon is probably a simplified version of a weapon common
during the Roman period.  The weapon could be aimed up and
down and side to side.  It had two separate bow arms  (oak) and
twisted skiens stretched across a wooden frame.  A crosspiece of
iron with a claw is held in place by two staples nailed to the stock.
An iron "key" with a length of rope served as a release mechanism.

Redrawn ad Enhanced - Marcus Audens

Reference: D. Nicolle, "Medieval Siege Weapons (2)," Osprey, 2003, N.V. 69