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

[265] Nay, he found by experience that the Jews fell more heavily upon him than did the Parthians, and created him troubles perpetually, and this ever since he was gotten sixty furlongs from the city; these sometimes brought it to a sort of a regular battle. Now in the place where Herod beat them, and killed a great number of them, there he afterward built a citadel, in memory of the great actions he did there, and adorned it with the most costly palaces, and erected very strong fortifications, and called it, from his own name, Herodium. Now as they were in their flight, many joined themselves to him every day; and at a place called Thressa of Idumea his brother Joseph met him, and advised him to ease himself of a great number of his followers, because Masada would not contain so great a multitude, which were above nine thousand. Herod complied with this advice, and sent away the most cumbersome part of his retinue, that they might go into Idumea, and gave them provisions for their journey; but he got safe to the fortress with his nearest relations, and retained with him only the stoutest of his followers; and there it was that he left eight hundred of his men as a guard for the women, and provisions sufficient for a siege; but he made haste himself to Petra of Arabia.