Ammianus writes of the catapult 1:
`In the middle of the ropes2 rises a wooden arm like a chariot pole . . . to the top of the arm hangs a sling . . . when the 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 it sting erect,3 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.’
Fig. 7. Catapult (with a sling) (See previous page)
A. The arm at rest, ready to be wound down by the rope attached to it and also to the wooden roller of the windlass. The stone may be seen in the sling. The upper end of the pulley rope is hitched by a metal slip-hook (fig.6) to a ring-bolt secured to the arm just below the sling.
B. The position of the arm when fully wound down by means of the windlass and rope. See also EE, fig. 8.
C. The position of the arm at the moment the stone D leaves the sling, which it does at an angle of about 45 degrees.
E. By pulling the cord E the arm B is at once released from the slip-hook and, taking an upward sweep of 90 degrees, returns to its original position at A.
THE SLING (OPEN)
F. Its fixed end which passes through a hole near the top of the arm.
G. The leather pocket for the stone.
H. The loop which is hitched over the iron pin at the top of the arm when the stone is in position in the sling, as shown at A and B, fig. 7.
1 Roman History, Book XXIII., Chapter IV.
2 i.e. in the middle of the twisted skein formed of ropes of sinew or hair.
3 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.
I. I. } II. II. } The side pieces III. IV. The large cross-pieces V. The small cross-pieces
The ends of the cross-piece beams are stepped into the side pieces.
AA. The skein of twisted cord.
BB. The large winding wheels. The skein is stretched between these wheels, its ends passing through the sides of the frame, and then through the wheels and over their cross-bars. (fg. 12.)
By turning with a long spanner (fig. 6.) the squared ends of the spindles DD, the pinion wheels CC rotate the large wheels BB and cause the latter to twist the skein AA, between the halves of which the arm EE is placed.
FF. The wooden roller which winds down the arm EE. (fig. 6.)
The roller is revolved by four men (two on each side of the engine) who fit long spanners on the squared ends of the iron spindle GG.