2. Between two axletrees a strong large iron bar 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 when wild asses are hunted, they throw the stones behind them by their kicks so as to pierce the chests of those who pursue them, or to fracture their skulls.
8. Now let us come to the battering ram. A lofty pine or ash is chosen, the top of which is armed with a long and hard head of iron, resembling a ram, which form has given the name to the engine. It is suspended from iron beams running across on each side, like the top of a pair of scales, and is kept in its place by ropes hanging from a third beam. A number of men draw it back as far as there is room, and then again drive it forward to break down whatever opposes it by mighty blows, like a ram which rises up and butts.
9. By the frequent blows of this rebounding thunderbolt, buildings are torn asunder and walls are loosened and thrown down. By this kind of engine, if worked with proper vigour, garrisons are deprived of their defences, and the strongest cities are laid open and sieges rapidly brought to a conclusion.
10. Instead of these rams, which from their common use came to be despised, a machine was framed called in Greek the helepolis, by the frequent use of which Demetrius, the son of king Antigonus, took Rhodes and other cities, and earned the surname of Poliorcetes.
11. It is constructed in this manner. A vast testudo is put together, strengthened with long beams and fastened with iron nails; it is covered with bullocks' hides and wicker-work made of freshly cut twigs, and its top is smeared over with clay to keep off missiles and fiery darts.