A small model I constructed for throwing a stone ball, one pound in weight, will attain a distance of 200 yards when used with an arm that has a cup for holding the ball, though when a sling is fitted to the arm the range of the engine is at once increased to 300 yards.
The only historian who distinctly tells us that the catapult of the Greeks and Romans had a sling to its arm, is Ammianus Marcellinus. This author flourished about 380 A.D., and a closer study of his writings, and of those of his contemporaries, led me to carry out experiments with catapults and balistas which I had not contemplated when my work dealing with the projectile engines of the Ancients was published.
Fig. 7.—Catapult (with a Sling). Side view of frame and mechanism.
Scale: ½ in. = 1 ft.
Ammianus writes of the catapult[7]:
‘In the middle of the ropes[8] rises a wooden arm like a chariot pole ... to 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 till it is almost level with the ground ... when the arm is set free it springs up and hurls forth from its sling the stone, which is certain to crush whatever it strikes. This engine was formerly called the “scorpion,” because it has its sting erect,[9] but later ages have given it the name of Onager, or wild ass, for when wild asses are chased they kick the stones behind them.’
[7] Roman History, Book XXIII., Chapter IV.
[8] i.e. in the middle of the twisted skein formed of ropes of sinew or hair.
[9] The upright and tapering arm of a catapult, with the iron pin on its top for the loop of the sling, is here fancifully likened to the erected tail of an angry scorpion with its sting protruding.