Siege Weapons
The Trebuchet
A trebuchet is a medieval siege warfare weapon used to break down the walls of castles.
It was the successor of the Catapult; it could take heavier rocks and projectiles, and fling them farther, with more accuracy.
It worked by dropping a great weight that was attached to the short end of a long lever-arm.
The long end of the lever was thereby raised with considerable velocity, pulling a sling that contained the projectile.
The sling would increase the effective length of the lever arm, adding even more speed to the projectile before the sling released it.
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The Ballista
The Ballista, also known as the Arbalist, was an ancient missile launcher designed to hurl long arrows or heavy balls.
The Greek version was basically a huge crossbow fastened to a mount.
The Roman ballista was powered by torsion derived from two thick skeins of twisted cords through which were thrust two separate arms joined at their ends by the cord that propelled the missile.
The largest could accurately hurl 60-lb (27-kg) weights up to about 500 yards (450 m).
The Catapult
Catapults were invented about 400 BC in the powerful Greek town Syracus under Dionysios I.
The Greek engineers first constructed a comparatively small machine, the Gastraphetus, sort of a crossbow. The gastraphetes was powered by a specially large composite bow.
The military effect of the new weapon during the siege of Motya (Sicily) 397 BC encouraged the Greek engineers to enlarge the machine further.
They put a larger gastraphetes on a carriage and added a windlass to cock the heavier machine. Certain physical barriers prevented further enlargement of the composite bow.
Therefore in mid-fourth century BC torsion springs were introduced instead of the composite bow. The torsion spring consisted of a bundle of rope made from horse-hair or sinew. Such a spring could be enlarged indefinitely.
The new catapults were equiped now with two torsion springs powering the two arms of the catapult. Very soon the new design superseded the old gastraphetes machines.
Alexander the Great already employed torsion spring catapults on his campaigns. All Hellenistic armies and all powerful Greek cities soon owned a park of torsion artillery.
