9. And while addressing them a fleet arrived equal to that of the mighty sovereign Xerxes, under the command of the tribune Constantianus, and Count Lucillianus; they threw a bridge over the broadest part of the Euphrates: the fleet consisted of one thousand transports, of various sorts and sizes, bringing large supplies of provisions, and arms, and engines for sieges, and fifty ships of war, and as many more suitable for the construction of bridges. IV. § 1. I am reminded by the circumstances to explain instruments of this kind briefly, as far as my moderate talent may enable me to do, and first I will set forth the figure of the balista. 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.