Flavius Josephus, The Wars of the Jews
William Whiston, A.M., Ed.

[283] Hereupon Vespasian comforted his army on occasion of what happened, and as he found them angry indeed, but rather wanting somewhat to do than any further exhortations, he gave orders to raise the banks still higher, and to erect three towers, each fifty feet high, and that they should cover them with plates of iron on every side, that they might be both firm by their weight, and not easily liable to be set on fire. These towers he set upon the banks, and placed upon them such as could shoot darts and arrows, with the lighter engines for throwing stones and darts also; and besides these, he set upon them the stoutest men among the slingers, who not being to be seen by reason of the height they stood upon, and the battlements that protected them, might throw their weapons at those that were upon the wall, and were easily seen by them. Hereupon the Jews, not being easily able to escape those darts that were thrown down upon their heads, nor to avenge themselves on those whom they could not see, and perceiving that the height of the towers was so great, that a dart which they threw with their hand could hardly reach it, and that the iron plates about them made it very hard to come at them by fire, they ran away from the walls, and fled hastily out of the city, and fell upon those that shot at them. And thus did the people of Jotapata resist the Romans, while a great number of them were every day killed, without their being able to retort the evil upon their enemies; nor could they keep them out of the city without danger to themselves.