is fastened, like a
great rule, round, smooth, and polished; from its centre a square pin
projects for some distance, hollowed out into a narrow channel down its
middle. This is bound by many ligatures of twisted cords: to it two
wooden nuts are accurately fitted, by one of which stands a skilful man
who works it, and who fits neatly into the hollow of the pin or pole a
wooden arrow with a large point; and as soon as this is done, some
strong young men rapidly turn a wheel.

3. When the tip of the arrow's point has reached the extremity of the
cords, the arrow is struck by a blow from the balista, and flies out of
sight; sometimes even giving forth sparks by its great velocity, and it
often happens that before the arrow is seen, it has given a fatal wound.

4. The scorpion, which they now call the wild-ass, is in the following
form. Two axletrees of oak or box are cut out and slightly curved, so as
to project in small humps, and they are fastened together like a sawing
machine, being perforated with large holes on each side; and between
them, through the holes, strong ropes are fastened to hold the two parts
together, and prevent them from starting asunder.

5. From these ropes thus placed a wooden pin rises in an oblique
direction, like the pole of a chariot, and it is so fastened by knotted
cords as to be raised or depressed at pleasure. To its top, iron hooks
are fastened, from which a sling hangs, made of either cord or iron.
Below the pin is a large sack filled with shreds of cloth, fastened by
strong ties, and resting on heaped-up turves or mounds of brick. For an
engine of this kind, if placed on a stone wall would destroy whatever
was beneath it, not by its weight, but by the violence of its
concussion.

6. Then when a conflict begins, a round stone is placed on the sling,
and four youths on each side, loosening the bar to which the cords are
attached, bend the pin back till it points almost upright into the air;
then the worker of the engine, standing by on high ground, frees by a
blow with the heavy hammer the bolt which keeps down the whole engine;
and the pin being set free by the stroke, and striking against the mass
of cloth shreds, hurls forth the stone with such force as to crush
whatever it strikes.

7. This engine is called a _tormentum_, because all its parts are
twisted (_torquetur_); or a scorpion, because it has an erect sting; but
modern times have given it the name of the wild-ass, because