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Early Roman ballistae

The early Roman ballistae were made of wood, and held together with iron plates around the frames and iron nails in the stand. The main stand had a slider on the top, into which were loaded the bolts or stone shot. Attached to this, at the back, was a pair of ' winches ' and a 'claw', used to ratchet the bowstring back to the armed firing position.

The slider passed through the field frames of the weapon, in which were located the torsion springs (rope made of animal sinew), which were twisted around the bow arms, which in turn, were attached to the bowstring.

Drawing the bowstring back with the winches twisted the already taut springs, storing the energy to fire the projectiles. The bronze or iron caps, which secured the torsion bundles were adjustable by means of pins and peripheral holes, which allowed the weapon to be tuned for symmetrical power and for changing weather conditions.

The ballista was a highly accurate weapon (there are many accounts of single soldiers being picked off by ballistarii), but some design aspects meant it could compromise its accuracy for range. The maximum range was over 500 yards (460 m), but the effective combat range for many targets was far shorter.

The Romans continued the development of the ballista, and it became a highly prized and valued weapon in the army of the Roman Empire.

It was used, just before the start of the Empire, by Julius Caesar during his conquest of Gaul and on both of his campaigns in subduing Britain.