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

[29] At length Zamaris the Babylonian, to whom Herod had given that country for a possession, died, having lived virtuously, and left children of a good character behind him; one of whom was Jacim, who was famous for his valor, and taught his Babylonians how to ride their horses; and a troop of them were guards to the forementioned kings. And when Jacim was dead in his old age, he left a son, whose name was Philip, one of great strength in his hands, and in other respects also more eminent for his valor than any of his contemporaries; on which account there was a confidence and firm friendship between him and king Agrippa. He had also an army which he maintained as great as that of a king, which he exercised and led wheresoever lie had occasion to march.