Weight 1 1/2 tons , Range with a 6 lb stone ball, 300 yards
1 Twisting up the skein of cord by means of the winches
2 Winding down the arm
3 Releasing the arm when fully wound down
Of machines formed on the sling principle, that called Onager may be regarded as typical of all the rest. Its force entirely depended upon the torsion of a short thick rope, acting upon a lever which described an arc of a vertical circle. The lever had attached to its free extremity a sling, or sometimes it merely terminated in a spoon-shaped cavity. When bent back, it was secured by a catch or trigger, and charged with a stone. On starting the catch by a blow with a mallet, the lever described its arc of a circle with great velocity, and projected the stone to a considerable distance.
The trebuchet was another war machine used extensively during the Middle Ages. Essentially, it was a seesaw. Weights on the short arm swung the long throwing arm.
The catapult was the howitzer, or mortar, of its day and could throw a hundred-pound stone 600 yards in a high arc to strike the enemy behind his wall or batter down his defenses. "In the middle of the ropes a wooden arm rises like a chariot pole," wrote the historian Marcellinus. "At the top of the arm hangs a sling. When battle is commenced, a round stone is set in the sling. Four soldiers on each side of the engine wind the arm down until it is almost level with the ground. When the arm is set free, it springs up and hurls the stone forth from its sling." In early times the weapon was called a "scorpion," for like this dreaded insect it bore its "sting" erect.
The ballista had horizontal arms like a bow. The arms were set in rope; a cord, fastened to the arms like a bowstring, fired arrows, darts, and stones. Like a modern field gun, the ballista shot low and directly toward the enemy.