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

[171] And when the bank was now raised, and brought nearer than ever to the battlements that belonged to the walls, Josephus thought it would be entirely wrong in him if he could make no contrivances in opposition to theirs, and that might be for the city's preservation; so he got together his workmen, and ordered them to build the wall higher; and while they said that this was impossible to be done while so many darts were thrown at them, he invented this sort of cover for them: He bid them fix piles, and expand before them the raw hides of oxen newly killed, that these hides by yielding and hollowing themselves when the stones were thrown at them might receive them, for that the other darts would slide off them, and the fire that was thrown would be quenched by the moisture that was in them. And these he set before the workmen, and under them these workmen went on with their works in safety, and raised the wall higher, and that both by day and by night, fill it was twenty cubits high. He also built a good number of towers upon the wall, and fitted it to strong battlements. This greatly discouraged the Romans, who in their own opinions were already gotten within the walls, while they were now at once astonished at Josephus's contrivance, and at the fortitude of the citizens that were in the city.