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

[435] Now of the five children which Herod had by Mariamne, two of them were daughters, and three were sons; and the youngest of these sons was educated at Rome, and there died; but the two eldest he treated as those of royal blood, on account of the nobility of their mother, and because they were not born till he was king. But then what was stronger than all this was the love that he bare to Mariamne, and which inflamed him every day to a great degree, and so far conspired with the other motives, that he felt no other troubles, on account of her he loved so entirely. But Mariamne's hatred to him was not inferior to his love to her. She had indeed but too just a cause of indignation from what he had done, while her boldness proceeded from his affection to her; so she openly reproached him with what he had done to her grandfather Hyrcanus, and to her brother Aristobulus; for he had not spared this Aristobulus, though he were but a child; for when he had given him the high priesthood at the age of seventeen, he slew him quickly after he had conferred that dignity upon him; but when Aristobulus had put on the holy vestments, and had approached to the altar at a festival, the multitude, in great crowds, fell into tears; whereupon the child was sent by night to Jericho, and was there dipped by the Galls, at Herod's command, in a pool till he was drowned.